. 


FIRSf 


IN 


GENERAL  SCIENCE 


A  FIRST  YEAR  COURSE 


IN 


GENERAL  SCIENCE 


BY 


CLARA  A.  PEASE 

OF  THE   HIGH   SCHOOL,   HARTFORD,   CONNECTICUT 


CHARLES  E.  MERRILL  COMPANY 

NEW  YORK  CHICAGO 


COPYRIGHT,     IQIS 
BY    CHARLES    E.     MERRILL    CO. 

f4] 


PREFACE 

IT  is  not  necessary,  in  this  period  of  the  making  of  high 
school  curricula,  to  show  that,  for  the  first  year  of  a  high 
school,  a  general  course  in  science  is  better  than  a  year's 
study  of  one  branch  of  science.  Without  discussion  of  the 
advisability  of  a  general  course,  therefore,  the  author  would 
state  her  reasons  for  the  wide  choice  of  subjects  considered 
in  this  book. 

For  pupils  who  complete  a  high  school  course,  the  study 
of  general  science  should  be  an  introduction  to  any  ordinary 
high  school  work  in  biology,  physics,  chemistry,  geology, 
and  astronomy.  No  pupil  can  study  all  of  these  subjects,  but 
he  can  learn  that  they  are  not  separate  sciences  but  branches 
of  science.  Whatever  branch  he  studies  later,  he  will  find 
that  the  course  in  general  science  has  given  him  the  elements 
of  the  other  divisions  which  dovetail  into  that  branch. 

To  suit  the  needs  of  pupils  who  are  not  able  to  finish 
a  high  school  course,  this  first  year  science  course  must  pre- 
sent a  comprehensive  view,  though  with  no  attempt  to  be 
complete. 

"The  proper  study  of  mankind"  for  the  pupil  at  the  age  of 
twelve  to  fourteen  years  seems  to  be  the  world  of  which  he 
is  a  part.  The  fact  that  the  earth,  important  as  it  is  to 
man,  is  not  the  only  nor  the  greatest  body  in  the  universe; 
that  it  is  not  an  independent  body  sufficient  unto  itself; 
and  that  its  influence  extends  to  other  bodies  —  these  are 
some  of  the  subjects  taken  up  in  the  first  chapters. 

Before  studying  the  ever-changing  surface  of  the  earth 
and  its  life,  there  must  be  a  study  of  matter  in  the  mass 
and  of  the  forces  which  act  upon  it  from  without;  also  of 

359^395 


4          F.msf''MAH'*GbtJRSE  IN. GENERAL  SCIENCE 

the  composition  of  matter  and  the  behavior  of  the  different 
kinds,  alone  and  in  combination. 

The  agencies  which  have  given  the  earth  its  beauty,  its 
wonders,  and  its  fitness  for  the  development  of  life  are  con- 
sidered in  chapters  on  physiography. 

The  living  part  of  the  earth  and  its  relation  to  other  forms 
of  matter  are  emphasized  in  the  later  chapters. 

It  would  not  be  right  to  call  these  chapters  astronomy, 
physics,  chemistry,  etc.,  because  no  complete  treatment  of 
these  subjects  is  attempted.  The  author  believes  it  wise, 
however,  to  use  the  necessary  scientific  terms  in  describing 
phenomena,  properties,  and  the  like,  instead  of  using  circum- 
locution in  order  to  keep  within  the  every-day  vocabulary 
of  a  young  pupil. 

It  has  seemed  important  to  provide  a  simple  laboratory 
course  which  is  connected  closely  with  the  text,  but  which 
may  be  omitted  without  any  break  in  continuity  of  subject. 
For  many  years  the  slogan  has  been  "  Study  the  thing  itself, 
not  study  about  it."  Efforts  to  follow  this  rule  have  led,  in 
many  cases,  to  a  disconnected  array  of  facts  learned  from 
observation  of  unrelated  subjects.  Such  a  course  has  no 
connecting  links.  The  laboratory  work  and  the  textbook 
should  be  closely  related  in  order  that  the  pupil  may  get 
the  full  value  of  the  science  course. 

The  Laboratory  Exercises  which  accompany  this  book  are 
designed : 

First:  to  fix  in  the  mind  of  the  pupil  important  prin- 
ciples and  facts  which  may  have  been  known  for  hundreds 
of  years,  rather  than  to  have  them  re-discovered  by  the 
pupil. 

Second:  to  teach  by  experiment  one  or  more  applications 
of  a  principle  and  leave  the  pupil  to  make  other  applications 
whenever  the  principle  again  comes  to  his  attention. 

Third:  to  accustom  the  pupil  to  follow  directions,  and 
to  make  and  record  accurately  observations  of  phenomena. 


PREFACE  5 

Fourth:  to  teach  the  pupil  to  draw  reasonable  conclusions 
from  his  own  or  reported  observations. 

The  accomplishment  of  these  things  is  a  valuable  asset 
to  the  pupil,  whatever  work  he  undertakes  in  the  future. 

Another  object  of  this  book  is  to  show  the  future  citizens 
of  this  country  the  wide  range  of  scientific  work  done  by  the 
government,  not  only  for  the  education  of  its  people,  but  for 
their  material  welfare.  The  work  of  the  Weather  Bureau, 
the  Naval  Observatory,  the  Geological  Survey,  and  the 
Divisions  of  Forestry  and  of  Plant  Industry,  are  all  brought 
to  the  attention  of  the  pupil,  and  material  furnished  by  these 
departments  is  used. 

The  planning  of  this  course  was  the  work  of  five  teachers 
of  experience  in  a  large  high  school.  Prior  to  the  publication 
of  the  textbook,  the  plan  was  followed  for  four  years  by 
teachers,  experienced  and  inexperienced,  with  great  success, 
if  we  may  judge  by  the  work  of  the  pupils  and  by  the  number 
who  have  continued  the  study  of  science  after  the  first  year 
course. 

The  author  makes  grateful  acknowledgment  to  many 
friends  who  have  assisted  in  the  preparation  of  this  book: 
first  of  all,  to  her  principal,  Mr.  Clement  C.  Hyde,  and  her 
associate  teachers  in  the  science  department  of  the  Hartford 
Public  High  School,  for  their  unfailing  consideration  and 
encouragement  while  she  was  doing  the  double  work  of  teach- 
ing and  developing  this  course  in  General  Science;  to  her 
former  teacher,  Professor  William  North  Rice,  of  Wesleyan 
University,  Middletown,  Conn.,  for  wise  counsel  on  many 
subjects;  and  to  Professors  Edward  L.  Rice  and  Lewis  G. 
Westgate  of  Ohio  Wesleyan  University,  Miss  Elisabeth  W. 
Stone,  and  Mr.  David  G.  Smyth  of  Hartford,  who  have  read 
and  criticized  portions  of  the  manuscript.  For  illustrations, 
grateful  acknowledgment  is  made  to  Professor  David  P. 
Todd  of  Amherst,  Mass.,  to  Dr.  Henry  Fairfield  Osborn  of 
the  American  Museum  of  Natural  History,  to  Professor 


6          FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

Lewis  G.  Westgate  of  Delaware,  Ohio,  to  Mr.  Harold  M. 
Hine  and  Mr.  Raymond  B.  Case  of  Hartford,  to  the  Century 
Company  of  New  York,  to  the  Warner  and  Swasey  Com- 
pany of  Cleveland,  Ohio,  to  the  Coe-Mortimer  Company 
of  New  York,  to  Forecaster  Neifert  of  the  Hartford  office 
of  the  Weather  Bureau,  to  the  Chamber  of  Commerce  of 
Colorado  Springs,  to  the  Denver  and  Rio  Grande  Railroad, 
to  the  United  States  Geological  Survey,  and  to  the  Forest 
Service. 


CONTENTS 

CHAPTER  PAGE 

I.    THE  EARTH'S  PLACE  IN  THE  UNIVERSE 13 

II.    THE  EARTH'S  NEAREST  NEIGHBORS:  THE  MOON  AND  THE 

PLANETS 33 

III.  MATTER  AND  ITS  PROPERTIES 46 

IV.  FORCE  AND  MOTION:  PHYSICAL  STATES  OF  MATTER    .     .  56 
V.    HEAT:  ITS  DISTRIBUTION  AND  MEASUREMENT   ....  71 

VI.       LIQUIDS    AND   THEIR   PROPERTIES 81 

VII.    PROPERTIES  OF  GASES;   THE   ATMOSPHERE;   ATMOSPHERIC 

PRESSURE  .....     . 93 

V11I.    WEATHER;  WINDS  AND  STORMS;  CLIMATE 107 

IX.     LIGHT       .V     ........ 120 

X.    ELECTRICITY  AND  MAGNETISM 128 

XI.     How  MATTER  CHANGES  .     .     .     .-...-;. 138 

XII.    THE  COMMON  ELEMENTS  OF  THE  EARTH .  147 

XIII.  SOME  COMPOUNDS  OF  COMMON  ELEMENTS 158 

XIV.  MINERALS  AND  ORES:  THEIR  VALUE  AND  SOURCE       .     .  167 
XV.    THE  CRUST  OF  THE  EARTH,  MAN'S  STOREHOUSE    .     .     .  177 

XVI.    CONTINENTS;  OCEANS      ..." 190 

XVII.    MOUNTAINS;  MINING;  FORESTRY 202 

XVIII.    TOPOGRAPHIC  MAPS .     .  216 

XIX.    EARTHQUAKES;  VOLCANOES 225 

XX.    RIVERS  AND  THEIR  WORK 233 

XXI.    GLACIERS  AND  LAKES  244 


8  CONTENTS 

CHAPTER  PAGE 

XXII.    LIVING  MATTER 254 

XXIII.  THE  LIFE  OF  A  PLANT 265 

XXIV.  REPRODUCTION  AND  DEVELOPMENT  OF  PLANTS  .     .     .     .  276 
XXV.    THE  LIFE  OF  AN  ANIMAL 289 

XXVI.    REPRODUCTION  AND  DEVELOPMENT  OF  ANIMALS     .     .     .  298 

INDEX      .     .     .     .     .  x.  307 


SUGGESTIONS   TO   TEACHERS 

A  FEW  suggestions  as  to  the  use  of  this  book  may  be  helpful 
to  the  teachers  who  are  using  it.  A  glance  will  show  that  it 
is  a  textbook  to  be  studied  —  not  a  reading  book.  The  text 
of  each  chapter  is  organized  in  sections,  which  are  numbered, 
and  the  subject  of  each  section  is  given  in  heavy  type.  This 
will  help  the  pupil  to  know  what  he  is  studying  about  before 
he  begins  a  new  subject. 

A  scientific  term  printed  in  heavy  type  usually  serves  to 
call  attention  to  a  definition  or  an  explanation  of  the  term 
in  the  same  sentence  or  closely  following  it.  This  seems,  for 
the  first  year  science  pupils,  a  better  way  to  learn  the  use 
of  words  than  by  consulting  a  glossary  or  a  dictionary.  It 
will  be  helpful  for  the  pupil  to  write  out  with  each  lesson  the 
definition  of  the  words  occurring  in  heavy  type.  That  gives 
him  practise  in  stating  definitions  in  good  form,  and  helps 
him  to  avoid  such  expressions  as  "a  force  is  when/'  "a 
mountain  is  where,"  etc. 

A  large  dictionary  —  not  one  of  the  "handy"  size  —  should 
be  a  constant  book  of  reference  for  words  not  strictly  scien- 
tific but  not  in  the  pupil's  every-day  vocabulary.  Pupils 
should  be  cautioned  not  to  take  the  first  definition  given  but 
to  look  for  a  distinction  between  general  and  scientific  use 
and  to  learn  the  latter  definition. 

The  exercises  at  the  end  of  each  chapter  are  not,  in  the 
ordinary  sense,  a  review  of  the  chapter.  They  are  more  in 
the  nature  of  a  test  to  see  if  the  pupil  can  apply  principles 
just  learned.  The  exercises  may  be  used  as  a  test  after 
completing  the  chapter,  or  may  be  selected,  a  few  at  a  time, 
to  accompany  the  subjects  to  which  they  apply.  Not  only 

9 


10        FIRST  YEAR  COURSE   IN   GENERAL  SCIENCE 

the  principles  of  that  chapter  are  involved  but  those  of 
earlier  chapters  also. 

The  diagrams  and  illustrations  are  provided  with  the 
expectation  that  they  will  make  clearer  the  teaching  of  the 
text  and  that  original  work  will  be  done  by  the  pupils  in 
answering  the  questions  which  accompany  them.  This  may 
be  assigned  as  written  work  to  be  brought  to  the  class  and 
there  used  in  various  ways  by  the  teacher. 

If  it  is  not  possible  to  take  a  whole  year  for  the  course,  it 
is  advised  that  the  work  be  done  thoroughly  as  far  as  time 
allows  and  then  dropped. 

The  references  to  laboratory  work  indicate  the  points  at 
which  the  author  thinks  it  best  to  have  the  exercises  per- 
formed. If  for  any  reason  it  is  not  possible  to  have  all  the 
students  do  all  the  work,  there  are  three  ways  of  using  labo- 
ratory exercises  to  advantage.  (1)  Have  one  or  two  pupils 
do  the  work,  while  the  others  make  notes  of  observations 
reported  to  them;  then  have  the  class  work  out  the  results 
from  the  data.  (2)  Let  the  teacher  do  the  work,  instead  of 
the  pupils,  and  then  proceed  as  in  the  first  case.  (3)  The 
teacher  may  discuss  with  the  class  the  directions  in  the 
Laboratory  Manual,  give  some  supposed  observations,  and 
have  the  pupils  finish  as  before.  This  last  and  least  desirable 
method  requires  no  special  apparatus  for  this  course  but 
presupposes  that  the  teacher  has  a  laboratory  knowledge  of 
the  subject.  Some  of  the  exercises  are  to  be  performed  out 
of  class  with  material  which  every  pupil  can  obtain  for 
himself. 

A  laboratory  exercise  in  science  may  be,  as  in  history  or 
literature,  the  study  of  a  subject  from  other  sources  than  the 
textbook.  A  rich  field  for  this  work  is  provided  in  various 
government  bulletins  of  the  Departments  of  Agriculture 
and  of  the  Interior.  Lists  of  these  bulletins  may  be  obtained 
from  the  departments  at  Washington  on  request,  and 
copies  of  such  as  are  wanted  will  be  furnished  to  a  school 


SUGGESTIONS    TO    TEACHERS  11 

free,  on  application  to  the  senator  or  representative  from 
the  district. 

Another  kind  of  work  which  may  be  included  under  labo- 
ratory exercises,  is  the  observation  of  industries  carried  on 
in  the  town  or  city.  Even  if  pupil  and  teacher  do  not  under- 
stand perfectly  all  operations  viewed  in  the  paper  mill,  thread 
or  cloth  factory,  dye  works,  foundry,  machine  shop,  or  other 
manufactory,  they  will  see  much  that  can  be  used  in  class 
to  illustrate  and  apply  the  principles  upon  which  those 
industries  depend.  Application  from  the  principal  of  a 
school  will  usually  gain  permission  for  a  small  group  of  pupils, 
accompanied  by  the  teacher,  to  visit  some  of  the  shops  in  the 
vicinity  of  the  school.  If  there  are  several  divisions  of  the 
class,  each  division  might  study  a  different  industry.  Each 
would  learn  something  of  value,  though  not  all  the  same 
thing^ 

Field  work  and  photographs  can  be  employed  to  supple- 
ment the  chapters  on  the  surface  features  of  the  earth; 
the  collection  and  recognition  of  minerals  and  rocks  will 
add  to  the  interest  of  some  chapters  which  have  little 
laboratory  work.  Observation  of  living  things  will  bring 
a  new  interest  to  outdoor  life.  In  fact,  anything  which 
encourages  comparison  and  observation  of  details  is  an 
aid  to  mental  development  as  well  as  an  assistance  in  sci- 
entific training. 


A  FIRST  YEAR  COURSE  IN 
GENERAL  SCIENCE 

CHAPTER  I 
THE  EARTH'S  PLACE  IN  THE  UNIVERSE 

1.  The  Earth  and  Other  Bodies.  —  Many  thousand 
years  ago  there  were  living  in  widely  separated  parts  of 
the  earth  various  groups  of  people.  Each  group,  knowing 
nothing  of  the  others,  supposed  that  it  contained  all  the 
inhabitants  of  the  earth.  These  early  peoples  thought  that 
the  earth  was  flat  and  that  if  they  should  go  beyond  the 
portion  they  knew  about,  they  would  reach  the  edge  and 
fall  off. 

They  had  various  beliefs  as  to  what  kept  the  earth  in 
place.  Some  thought  it  rested  upon  the  shoulders  of  a 
giant,  and  some  upon  a  turtle's  back;  others  believed  it 
was  suspended  from  above. 

As  men  ventured  farther  from  home,  they  found  that 
there  were  other  peoples,  that  the  earth  was  larger  than 
they  had  supposed,  and  that  if  they  went  far  enough  in 
any  direction,  they  came  to  the  sea.  They  ventured  out 
upon  the  sea,  but  always  returned  over  nearly  the  same 
route  by  which  they  had  gone.  They  still  thought  that 
the  earth  was  flat. 

Their  ideas  of  the  motion  of  the  sun^and  stars  were  as 
simple  as  their  other  beliefs.  They  thought  that  these 
bodies  moved  daily  over  the  earth,  coming  from  the 
desert  plain  or  from  behind  the  mountains  or  out  of  the 
ocean,  according  to  their  point  of  observation. 

13 


14        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

Not  until  about  five  hundred  years  ago  did  any  one 
suspect  that  the  earth  was  like  a  globe  or  that  it  moved. 
More  has  been  learned  about  the  earth  since  the  days 
when  Columbus  repeated  to  his  timid  captains  the  order, 
"Sail  on,"  than  had  been  learned  in  all  the  time  before. 
Since  that  wonderful  voyage,  men  have  traveled  over  land 
and  water  around  the  earth  and  back  to  the  place  from 
which  they  started.  They  have  found  that  there  is  no 
"edge,"  and  that  at  no  point  does  the  earth  rest  upon  or 
touch  any  other  body. 

We  know  that  there  are  other  bodies,  for  when  we  look 
away  from  tfhe  earth,  we  see  many  luminous  or  light- 
giving  points,  and  we  see  two  bodies  whose  shape  we  can 
determine.  Men  have  been  watching  and  studying  these 
bodies  for  thousands  of  years.  The  ancients  learned 
much  that  was  interesting  about  them.  Modern  ob- 
servers have  learned  infinitely  more,  and  there  is  still  a 
great  deal  to  be  learned.  Some  bodies  are  known  to  be 
entirely  unlike  the  earth;  a  few  are  in  some  respects  similar 
to  the  earth;  but  there  has  never  been  found  any  body  in 
external  condition  exactly  like^the  earth. 

The  place  where  these  luminous  bodies  seem  to  be  is 
called  the  sky,  or  the  heavens,  and  the  bodies  are  called  the 
heavenly  bodies.  The  sky  looks  like  the  inside  of  a  great 
dome,  where  in  the  daytime  we  usually  see  but  one  bright 
body,  the  sun,  which  to  us  is  by  far  the  most  important  of 
all  the  heavenly  bodies.  At  night  we  see  stars,  planets,  the 
moon,  and  occasionally  a  comet,  meteors,  and  shooting  stars. 

2.  The  Number  of  the  Stars.  —  The  stars  are  the  most 
numerous  of  the  heavenly  bodies,  but  it  is  not  strictly  true 
to  say  that  the  number  visible  to  us  is  countless. 

In  the  whole  sphere  of  the  heavens,  there  are  only  about 
7,000  stars  bright  enough  to  be  seen  without  a  telescope  on 
a  clear,  moonless  night.  Half  of  that  number  are  in  the 
part  of  the  sky  that  is  visible  to  dwellers  in  the  northern 


THE  EARTH'S  PLACE  IN  THE  UNIVERSE  15 

hemisphere;  but  because  of  dust  and  vapor  in  the  atmos- 
phere, the  number  of  these  stars  that  can  readily  be  seen  is 
reduced  to  about  2,500.  The  use  of  an  opera  glass  or  a 
small  telescope  reveals  many  which  cannot  be  seen  by  the 
naked  eye.  In  the  whole  sky,  with  the  largest  telescope, 
100,000,000  may  be  seen.  The  stars  look  like  bright  points 
and  twinkle  most  perceptibly  when  they  are  near  the 
horizon,  which  is  the  circle  where  earth  and  sky  seem  to 
meet. 

3.  Constellations.  —  Certain  groups  of  bright  stars  near 
together  are  known  as  constellations.  The  people  of  ancient 
times  gave  names  to  these  groups,  sometimes  in  memory  of 


FIG.  1.  — SCORPIO    • 

The  constellation  Scorpio  may  be  seen  in  the  southern  part  of  the  sky 
during  the  summer.  At  9  p.  m.  at  the  middle  of  July,  the  brightest  star, 
Antares,  is  directly  over  the  southern  point  of  the  horizon. 

a  hero  or  of  an  event.  The  brighter  stars  in  a  constellation 
outline  an  object  or  designate  the  position  of  some  important 
part  of  the  body  of  a  man  or  animal.  Aldebaran  is  a  star 
in  the  eye  of  Taurus,  the  bull,  and  the  cluster  called  the 
Pleiades  is  in  his  shoulder. 

Orion  is  farther  south  than  Taurus  and  rises  a  little  later. 
He  is  a  hunter  who  has  his  club  raised  to  strike  the  bull. 


16        FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 

The  "belt  of  Orion"  consists  of  three  stars  in  a  straight 
line,  nearly  perpendicular  to  the  eastern  horizon  as  the  con- 
stellation rises.  Below  and  nearly  at  right  angles  to  the 
belt  are  three  fainter  stars  called  his  sword.  In  northern 
countries  Orion  and  Taurus  are  seen  in  the  east  early  in  the 
evening  in  November  and  December. 

Orion  is  followed  by  two  dogs.  In  Canis  Major,  the 
larger  dog,  is  the  star  Sirius,  which  is  also  called  the  Dog  Star. 
It  is  the  brightest  star  in  the  whole  sky  and  is  visible  nearly 
all  winter.  In  summer  it  is  in  the  same  part  of  the  sky  as 
the  sun,  and  is  shining  on  us  during  the  day,  but  is  invisible 
because  of  the  brighter  light  of  the  sun.  The  period  known 
as  "dog  days"  gets  its  name  from  the  fact  that  the  Dog 
Star  is  then  shining  upon  the  earth  in  the  daytime. 

Late  in  the  spring  in  northern  latitudes,  Leo,  the  lion, 
is  almost  directly  overhead.  It  can  be  recognized  by  a  part 
of  the  constellation  shaped  like  a  sickle  or  grass  hook.  The 
star  in  the  end  of  the  handle  is  the  brightest  in  the  group 
and  is  called  Regulus.  The  northern  crown,  Corona,  is  an- 
other summer  constellation.  It  lies  east  of  Leo  and  may  be 
identified  by  its  shape  —  that  of  a  wreath  or  crown. 

Scorpio,  the  scorpion,  is  the  most  brilliant  summer  con- 
stellation and  may  be  identified  by  its  kite-shaped  figure. 
Antares,  a  reddish  star,  is  located  where  the  tail  joins  the 
body  of  the  kite.  Scorpio  is  seen  in  the  south  in  August 
and  is  never  high  above  the  horizon  in  the  latitude  of  the 
northern  states. 

4.  To  Find  the  North  Star.  —  Look  in  the  northern  part 
of  the  sky  for  a  group  of  seven  stars  which  outline  the  form 
of  a  long-handled  dipper.  This  group  is  called  the  Big  Dip- 
per. The  two  stars  on  the  side  of  the  bowl  farther  from  the 
handle  are  called  the  pointers,  because  a  line  drawn  through 
them  points  to  the  North  Star.  This  imaginary  line, 
extended  northward  for  about  five  times  the  distance  be- 
tween the  pointers,  passes  very  near  the  North  Star.  This 


THE  EARTH'S  PLACE  IN  THE  UNIVERSE 


17 


is  the  only  star  near  the  line  which  is  as  bright  as  the 
pointers. 

5.  Stars  Visible  all  the  Year.  —  The  constellations  in 
the  northern  sky  are  visible  any  clear  night  in  the  year  from 
all  places  in  the  northern  hemisphere. 

Three  well-known  groups  are  the  Great  Bear,  the  Little 
Bear,  and  Cassiopeia  (sometimes  called  Cassiopeia  in  her 


FIG.  2. —  THE  BIG  DIPPER  AND 
THE  NORTH  STAR 

Distances  in  the  sky  are  meas- 
ured in  degrees  (1°  =  1/360  of  a 
circle).  The  pointers  are  5°  apart; 
using  this  distance  as  a  measure, 

1.  Estimate  the  distance  between 
the  stars  at  the  top  of  the  Dipper; 

2.  From  either  pointer  in  a  straight 
line  to  the  end  of  the  handle;    3. 
From  the  North  Star  to  the  farther 
pointer. 


*  North  Star 


*      * 


Chair).  A  part  of  the  Great  Bear  is  known  as  the  Big  Dip- 
per, and  the  tail  of  the  bear  is  the  handle  of  the  dipper.  The 
tail  of  the  Little  Bear  makes  the  handle  of  the  Little  Dipper, 
and  the  North  Star  is  at  the  end  of  the  tail.  Except  for  the 
stars  that  form  the  outlines  of  the  dippers,  there  are  no 
conspicuous  stars  in  the  constellations  of  the  bears. 

To  locate  Cassiopeia,  imagine  a  circle  around  the  North 
Star  passing  through  the  bowl  of  the  Big  Dipper.  Look 
about  half-way  around  the  circle  from  the  bowl  and  you  find 
an  open,  sprawling,  W-shaped  figure.  This  is  the  brightest 
part  of  the  chair.  (LABORATORY  MANUAL,  Exercise  I.) 


18        FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 

6.  Reasons  for  Studying  Constellations.  —  If  we  are 
moving  smoothly  along  in  a  train,  it  is  sometimes  necessary 
to  look  at  a  stationary  object  in  order  to  realize  our  own 
motion.  In  the  same  Way,  observation  of  stars  which  are 


NORTHERN  HORIZON 

FIG.  3. — THE  NORTHERN  SKY 

Copy  or  trace  the  diagram  of  the  northern  sky.  Draw  a  line 
through  the  Pointers  and  the  North  Star  across  the  circle.  Draw  a 
line  at  right  angles  to  this  line,  also  passing  through  the  North  Star. 

1.  What  group  is  in  the  same  quarter  as  tho  Big  Dipper?  2.  In 
what  quarter  is  Cassiopeia's  Chair? 

stationary  helps  us  to  realize  the  motion  of  the  earth.  Many 
stars  are  so  much  alike  that  it  is  difficult  to  find  the  same 
star  we  observed  a  week  or  a  month  ago  unless  it  forms  a 
part  of  some  group  of  definite  shape.  When  we  have  learned 


THE  EARTH'S   PLACE  IN  THE  UNIVERSE  19 

to  recognize  the  groups,  it  is  easy  to  find  the  "star  in  the  end 
of  the  dipper  handle,"  "the  brightest  star  in  Taifrus,"  or 
"the  belt  of  Orion,"  even  if  the  group  is  in  a  different 
part  of  the  sky  from  that  in  which  we  saw  it  last. 

Another  reason  why  we  should  know  something  about  the 
constellations  is  the  fact  that  references  to  the  stars  are 
found  in  the  poetry  and  the  history  of  all  ages  since  men 
began  to  express  their  thoughts  and  record  their  observations 
in  writing.  We  can  better  understand  these  references  if 
we  know  the  stars  which,  long  before  the  pyramids  of  Egypt 
were  built,  were  shining  upon  the  earth  just  as  they  are  to- 
day. Many  of  the  names  by  which  the  stars  were  known 
to  the  Persians,  the  Egyptians,  and  the  Greeks  have  been 
handed  down  to  us. 

7.  The    Brightness    of    the    Stars.  —  Early  astronomers 
thought  the  brightness  of  stars  was  due  to  their  size,  so  they 
called  the  brightest  ones  first-magnitude  stars,  those  a  little 
less  bright  second-magnitude  stars,  and  so  on  down  to  the 
sixth  magnitude.     In  the  city,  where  there  is  so  much  arti- 
ficial light,  we  rarely  see  stars  fainter  than  those  of  the  third 
magnitude.     Sirius,  Vega,  Regulus,  and  Aldebaran  are  first- 
magnitude  stars;    the  North  Star  and  the  stars  of  the  Big 
Dipper  and  of  Cassiopeia  are  some  of  the  second-magnitude 
stars. 

It  is  now  known  that  the  brightness  of  a  star  depends  not 
only  on  its  size,  but  on  its  distance  from  the  earth  and  on  its 
temperature.  Many  of  the  stars  are  larger  than  the  sun 
but  are  much  more  distant;  they  seem  to  us  like  mere  points 
of  light.  Enough  has  been  learned  about  the  stars  to  make 
it  clear  that  they  are  very  unlike  the  earth  in  size,  tempera- 
ture, and  condition. 

8.  The    Distance    of    the    Stars.  —  The  stars  are  so  far 
away  that  their  distances  cannot  be  expressed  in  any  number 
that  we  can  comprehend.     When  we  say  that  the  nearest 
star  is  millions  of  millions  of  miles  away,  it  is  impossible  to 


20        FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 

realize  what  these  words  mean.  Supposing  that  an  express 
train  were  traveling  every  day  a  thousand  miles  (about 
the  distance  from  Chicago  to  Boston),  it  would  take  two 
years  and  nine  months  to  travel  one  million  miles. 

Light  passes  from  one  place  to  another  so  rapidly  that 
we  think  of  its  passage  as  instantaneous,  that  is,  as  taking 
no  time  at  all.  It  has  been  proved,  however,  that  light 
takes  eight  minutes  to  come  from  the  sun  to  the  earth, 
nearly  ninety-three  millions  of  miles.  The  nearest  star  is 
so  far  away  that  its  light  takes  more  than  four  years  to 
come  from  the  star  to  the  earth.  The  light  that  we  re- 
ceive from  the  North  Star  to-night  started  nearly  seventy 
years  ago.  Many  stars  are  much  more  distant. 

9.  Why  we  should  Know  the  North  Star. —  For  de- 
termining direction,  especially  in  navigation,  the  North  Star 
is  of  very  great  importance.  It  is  so  situated  that  at  most 
places  north  of  the  equator  it  can  be  seen  in  the  northern 
part  of  the  sky  throughout  any  clear  night  in  the  year.  It 
does  not  seem  to  change  its  position  from  hour  to  hour,  as 
other  stars  do.  The  North  Star  is  also  called  Polaris,  or  the 
Pole  Star,  because  the  imaginary  axis  of  the  earth,  if 
extended  from  the  north  pole,  would  pierce  the  sky  very 
near  to  this  star.  The  stars  in  the  northern  sky  seem  to 
revolve  about  the  Pole  Star,  just  as  all  the  lands  near  the 
north  pole  of  a  terrestrial  globe  seem  to  revolve  around  that 
point  as  the  globe  is  rotated. 

When  we  are  looking  directly  at  the  North  Star,  we  are 
facing  north,  and  the  point  on  the  horizon  in  a  vertical  line 
below  the  star  is  the  north  point.  As  one  travels  northward, 
the  North  Star  seems  to  rise  higher  and  higher  above  the 
horizon.  Commodore  Peary  must  have  seen  it  at  the  zenith, 
—  that  is,  directly  overhead  —  when  he  reached  the  north 
pole  in  1909.  He  was  then  ninety  degrees  from  the  equator, 
and  the  distance  from  the  horizon  to  the  zenith,  where  he  saw 
the  North  Star,  is  ninety  degrees.  The  number  of  degrees  of 


THE  EARTH'S  PLACE  IN  THE  UNIVERSE  21 

the  North  Star  above  the  horizon  is  always  the  same  as  the 
number  of  degrees  of  the  observer  from  the  equator. 

10.  The  Motion  of  the  Stars,  Apparent  from  Hour  to  Hour. 
If  we  should  watch  the  Dipper  all  night,  we  should  find 
that  it,  and  all  other  stars  in  the  vicinity,  appear  to  move  in 
a  circle  around  the  Pole  Star  in  a  direction  opposite  to  that 
of  the  hands  of  a  clock.     Other  stars,  which  we  saw  in  the 
east  in  the  early  evening,  would  rise  higher,  pass  overhead, 
and  set  in  the  west,  all  moving  in  the  same  direction  as  the 
Dipper.     At  the  end  of  a  day  (twenty-four  hours),  we  should 
see  each  group  almost  where  it  was  at  the  beginning.     This 
apparent  westward  motion  of  the  stars  is  due  to  the  fact  that 
the  earth  is  turning  about  its  axis,  always  toward  the  east. 
This  motion  of  the  earth  makes  the  sun  in  the  day,  and  the 
moon  and  stars  at  night,  seem  to  move  toward  the  west. 

11.  The  Change  in  the  Position  of  the  Stars,  Apparent 
from  Month  to  Month.  —  If,  instead  of  observing  the  posi- 
tion of  the  stars  from  hour  to  hour,  we  watch  them  at  the 
same  hour  of  the  evening  from  month  to  month,  we  shall  see 
that  a  group  of  stars,  as  the  Dipper  or  the  Sickle  or  Orion, 
has  moved  from  its  earlier  position  and  that  another  constel- 
lation has  taken  its  place. 

People  of  ancient  times  reckoned  the  seasons  by  the  posi- 
tions of  stars.  In  the  same  month  of  every  year,  a  certain 
constellation  is  seen  in  the  east  as  soon 'as  it  is  dark:  Leo  in 
the  spring,  Scorpio  in  the  early  summer,  and  Taurus  and 
Orion  in  the  fall  and  winter.  This  change  of  position, 
which  gives  a  different  appearance  to  the  sky  at  different 
seasons,  is  due  to  the  motion  of  the  earth  around  the  sun. 
It  moves  eastward  in  its  annual  journey  around  the  sun  and 
thus  changes  its  position  with  relation  to  the  stars.  At 
the  end  of  a  year,  a  given  group  will  be  found  again  where 
it  was  seen  at  the  beginning  of  the  year. 

The  rotation  of  the  earth  about  its  axis  causes  changes  of 
position  which  can  be  observed  from  hour  to  hour;  the 


22        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

revolution  around  the  sun  causes  changes  of  position  which 
are  apparent  from  month  to  month.  The  motions  of  the 
stars  are  always  apparently  westward,  .because  the  earth's 
motion  around  the  sun  is  eastward. 

12.   The    Solar    System.  —  The  sun  is  a  moderate-sized 
star,  very  much  nearer  to  us  than  any  other  star.     There 


FIG.  4.  —  THE   SIZE   OF  THE   SUN   COMPARED   WITH  THE   DISTANCE 
FROM  THE  EARTH  TO  THE  MOON 

Imagine  the  earth  at  the  center  of  the  sun's  sphere  and  the  moon 
revolving  around  the  earth  on  the  circle  within.     Measure  from  E  to  M. 

1.  What  fraction  of  the  radius  of  the  sun  is  the  distance  from  E  to  M? 

2.  If  E  to  M  is  240,000  miles,  what  is  the  diameter  of  the  sun?    3.  At  the 
rate  of  1,000  miles  a  day,  how  long  would  it  take  the  earth  to  travel  across 
the  sun's  disk? 

are  other  bodies,  called  planets,  revolving  about  the  sun; 
and  other  smaller  bodies,  called  satellites,  revolving  about 
some  of  the  planets.  The  sun  and  the  planets  with  their 
satellites  make  up  the  solar  system. 

While  the  planets  are  revolving  around  the  sun,  they  and 
their  satellites  are  rotating  upon  their  axes,  each  body  having 
a  definite  period  or  time  of  rotation. 


THE  EARTH'S  PLACE  IN  THE  UNIVERSE  23 

There  is  no  star  within  millions  of  millions  of  miles  of  the 
solar  system,  and  except  an  occasional  comet  or  meteor, 
nothing  ever  enters  the  vast  space  between  the  solar  system 
and  the  stars. 

13.  The    Sun.  —  By  far  the  largest  and  most  important 
body  in  the  solar  system  is  the  sun.     Its  diameter  is  more 
than  one  hundred  times  that  of  the  earth.     The  distance 
from  the  center  of  the  sun  to  its  surface  is  nearly  twice  the 
distance  from  the  earth  to  the  moon. 

The  interior  of  the  sun  is  thought  to  be  like  a  heavy, 
white-hot  liquid,  but  the  outer  portions,  which  we  see,  are 
known  to  be  intensely  heated  gases.  The  sun  is  composed 
of  the  same  elements  as  the  earth,  but  the  condition  of  these 
elements  is  so  different  that  they  can  be  recognized  only  by 
means  of  an  instrument  for  the  study  of  light,  called  the 
spectroscope.  %  It  is  not  known  just  what  makes  the  sun  hot, 
but  it  is  known  that  it  is  not  a  burning  body  as  some 
people  have  supposed.  The  condition  of  the  sun  is  like 
that  of  the  stars.  It  is  so  near  us  that,  by  looking  through 
smoked  or  colored  glass,  we  are  able  to  see  its  shape  and 
apparent  size.  It  looks  about  the  size  of  the  full  moon, 
but  is  really  very  many  times  as  large. 

14.  Day    and    Night.  —  We  learned  when  we  were  very 
young  that  the  earth  rotates  on  its  axis,  once  in  twenty- 
four  hours.      It  is  this  rotation  which  makes  it  seem  as  if 
the  sun  rises  in  the  east,  passes  across  the  sky,  and  then 
sinks   below  the  western  horizon.      Half  of   the   earth   is 
turned    toward    the    sun    and    hence    is    lighted    at    one 
time;  in  that  half  it  is  day,  while  in  the  unlighted  half  it 
is  night.     At  the  moment  the  sun  is  rising  at  a  given  place, 
there  are  180  degrees  of  unlighted  earth  to  the  west  of  that 
place  and  180  degrees  of  daylight  to  the  east.     The  light  is 
constantly  advancing  toward  the  west  and  retreating  from 
the  east.     Places  where  the  sun  is  setting  are  half-way  around 
the  earth  from  places  where  it  is  rising. 


24        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

15.  The  Cause  of  Seasons.  —  The  unequal  length  of  day 
and  night  and  the  change  of  seasons  depend  on  the  position 
of  the  earth's  axis.  To  illustrate  conditions,  draw  upon  a 
table  as  large  a  circle  as  possible,  to  represent  the  orbit  or 
path  of  the  earth  around  the  sun.  The  table  is  the  plane 
in  which  the  circle  lies,  that  is,  the  plane  of  the  orbit. 
At  opposite  sides  of  the  circle,  mark  Spring  and  Autumn. 
Darken  the  room  and  place  a  candle  or  low  lamp  in  the 
center  of  the  circle  to  represent  the  sun.  Let  a  tennis  ball 
represent  the  earth.  Mark  opposite  points  on  the  ball  N 
and  S.  Pass  a  knitting  needle  through  these  two  points,  as 
the  axis.  Holding  the  axis  perpendicular  to  the  table  at 
Spring,  we  see  that  the  ball  is  lighted  from  the  point  N  to 
the  point  S,  most  brightly  half-way  between.  Keeping  the 
axis  perpendicular,  move  slowly  around  the  circle,  turn- 
ing the  ball  at  the  same  time.  It  is  all  the  time  lighted 
just  as  at  first  —  one  half  light,  the  other  half  dark,  with 
the  points  N  and  S  marking  the  extent  of  light  in  each 
direction. 

If,  now,  the  axis  is  tipped  so  that  it  makes  less  than  a  right 
angle  with  the  table,  and  the  ball  is  placed  at  Spring,  we  see 
that  it  is,  as  before,  lighted  from  N  to  S  and  most  brightly 
at  the  line  half-way  between.  But  as  we  move  around  the 
circle,  keeping  the  axis  always  pointing  in  the  same  direction, 
conditions  change.  At  one  position  the  north  pole  is  turned 
away  from  the  sun;  then  there  is  no  light  at  the  north  pole, 
but  there  is  light  all  around  the  south  pole.  At  the  opposite 
point  on  the  circle,  the  reverse  is  true. 

The  facts  in  regard  to  the  earth  are  these:  its  axis  is  in- 
clined 23J°  to  the  plane  of  the  earth's  orbit,  and  always 
points  in  the  same  direction  —  almost  directly  to  the  North 
Star.  Hence,  the  north  pole  is  sometimes  turned  away  from 
the  sun,  sometimes  toward  it.  On  two  days,  one  in  March 
and  one  in  September,  the  sun's  rays  fall  vertically  upon  the 
equator  and  obliquely  90°  north  and  south  of  the  equator, 


THE  EARTH'S  PLACE  IN  THE  UNIVERSE  25 

that  is,  as  far  as  the  poles.  Daylight  then  extends  to  both 
poles,  and  day  and  night  are  equal  everywhere. 

All  that  has  been  said  about  the  direction  of  the  light 
is  also  true  about  the  heat  received  from  the  sun.  From 
spring  to  autumn,  the  north  pole  is  turned  toward  the  sun. 
The  sun's  rays,  giving  light  and  heat,  are  then  received  ver- 
tically at  places  in  the  torrid  zone  north  of  the  equator,  and 
obliquely  at  places  within  a  distance  of  90°,  that  is,  reaching 
to  places  beyond  the  north  pole.  It  is  summer  in  northern 
latitudes,  and  the  days  are  longer  and  warmer  there  than 
in  the  other  half  of  the  earth.  Just  the  reverse  is  true  in 
the  period  between  autumn  and  spring.  It  is  winter  in 
northern  latitudes,  and  the  days  there  are  shorter  and 
colder  than  in  southern  latitudes. 

16.  The  Circles  and  Zones  of  Light.  —  If,  by  drawing 
a  line  upon  the  earth,  we  could  connect  all  the  places  where 
the  sun  shines  vertically  at  noon  on  March  21,  we  should 
have  a  circle  around  the  earth  equally  distant  from  both 
poles.  Because  it  is  equidistant,  it  is  called  the  equator. 

A  similar  circle  drawn  on  June  21  gives  the  tropic  of 
Cancer,  23 1°  north  of  the  equator.  The  sun  never  shines 
vertically  any  farther  north  than  the  tropic  of  Cancer.  On 
June  21,  it  shines  obliquely  upon  the  earth  beyond  the 
north  pole  just  as  far  as  the  tropic  of  Cancer  is  north 
of  the  equator  —  that  is,  23 J°.  Consequently  the  arctic 
circle  marks  the  line  23J°  from  the  pole  and  66|°  from  the 
equator. 

Within  the  arctic  circle  the  sun  is  visible  every  day  during 
the  six  months  of  summer,  and  during  the  winter  it  nowhere 
comes  above  the  horizon  for  more  than  a  short  time  each 
day.  At  the  north  pole  it  is  visible  for  the  whole  day  during 
the  summer  and  is  not  seen  at  all  during  the  winter.  The 
nearer  a  place  is  to  the  pole,  the  longer  are  its  summer  days 
and  the  shorter  its  winter  days.  At  Hammerfest,  Norway, 
the  most  northern  town  of  Europe,  the  sun  never  sets  from 


26        FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 

May  13  to  July  29,  and  it  never  rises  from  November  18 
to  January  23. 

17.  The  Place  of  Sunrise.  —  In  March,  when  the  sun 
is  over  the  equator  and  midway  between  the  north  and  south 
poles,  it  rises  everywhere  exactly  in  the  east,  midway 
between  the  north  and  south  points  on  the  horizon. 


FIG.  5. — THE  PLACE  OP  SUNRISE 

1.  If  you  were  playing  tennis  on  a  spring  morning  at  a  position  on  the 
line  EW,  what  would  be  the  best  direction  to  face?  Why?  2.  What  posi- 
tion would  be  least  favorable  for  a  player  during  an  autumn  forenoon? 
Why?  3.  In  the  afternoon  in  summer? 

[This  picture  is  from  A  New  Astronomy  by  David  Todd.  Copyright, 
1897  and  1906,  by  American  Book  Company.  Reproduced  by  permission.] 

During  the  spring  months  it  shines  each  day  over  places 
farther  north  of  the  equator,  because  its  place  of  rising  is 
each  day  farther  north  of  the  east  point,  until  June  21, 
when  it  rises  23J°  north  of  east.  In  the  early  summer 
only,  in  the  northern  hemisphere,  does  the  morning  sun 
shine  even  obliquely  into  windows  on  the  north  side  of 


THE  EARTH'S  PLACE  IN  THE  UNIVERSE  27 

the  house.  Again  in  September  the  sunrise  is  at  the  east 
point,  but  each  day  afterward  it  is  farther  south  of  east, 
until  December  21,  when  it  is  23  J°  south  of  east.  South 
windows  then  get  sunshine  very  early  in  the  forenoon 
and  long  after  midday. 

18.  The  Sun's  Position  at  Noon.  —  Next  in  importance 
to  the  position  of  the  North  Star  is  the  position  of  an  imagi- 
nary line  called  the  celestial  meridian.  This  is  a  circle  pass- 
ing through  the  north  point  on  the  horizon,  the  zenith,  and 
the  south  point,  and  then  around  the  other  side  of  the  earth 
to  the  north  point.  It  divides  the  sky  into  an  east  and  a 


North  Star 


FIG.  6. — THE  CELESTIAL  MERIDIAN 

1.  What  part  of  a  circle  does  the  line  NZS  form?  2.  How  many  degrees 
from  N  to  Z?  3.  If  the  observer  (O)  is  in  lat.  30°,what  is  the  position  of  the 
North  Star  on  the  meridian?  (Answer  in  degrees  from  the  nearest  letter.) 
4.  The  equator  of  the  sky  is  about  90°  from  the  North  Star;  locate  the  place 
where  it  crosses  the  meridian,  in  the  same  way  that  you  answered  3.  5.  At 
what  times  in  the  year  is  the  sun  on  the  equator? 

west  half;  and  since  the  circle  always  'passes  through  the 
zenith,  there  is  a  celestial  meridian  for  every  observer. 
When  the  sun  or  the  moon  crosses  the  meridian,  it  has 
made  half  its  daily  journey  from  rising  to  setting.  The 
abbreviations  a.  m.  and  p.  m.  refer  to  the  time  when  the 
sun  crosses  the  meridian.  The  letters  a.  m.  stand  for  the 
Latin  ante  meridiem,  before  midday;  p.  m.  for  post  meridiem, 
after  midday. 

At  noon  the  sun  is  on  the  meridian  over  the  south  point 
in  the  horizon.  In  northern  latitudes  it  is  higher  above 
the  horizon  at  noon  in  June  than  at  any  other  time  in  the 


28        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

year,  but  even  then  the  sun  is  not  exactly  overhead 
at  any  place  north  of  the  tropic  of  Cancer.  If  it  were  so, 
there  would  be  no  " shady  side  of  the  house"  at  noon.  The 
sun  is  nearer  the  southern  horizon  at  noon  in  December  than 
at  any  other  time,  and  in  March  and  September  it  is  half- 
way between  its  positions  in  June  and  December.  (LABO- 
RATORY MANUAL,  Exercise  II.) 

19.  Latitude  and  Longitude.  —  We  have  been  accustomed 
to  learn  the  latitude  and  longitude  of  a  place  from  a  map  in 
a  geography  without  thought  as  to  how  these  facts  are  known. 
The  latitude  and  longitude  of  a  place  were  originally  deter- 
mined by  observations  upon  the  position  of  the  sun  and  stars 
as  seen  from  that  place,  or  as  calculated  from  an  observatory 
whose  exact  distance  and  direction  from  that  place  were 
known. 

Sea  captains  find  the  latitude  and  longitude  of  their 
vessels  by  observations  made  daily,  and  if  for  some  days 
neither  sun  nor  stars  are  visible,  a  ship  may  go  far  out  of  her 
course.  The  United  States  government  employs  astrono- 
mers at  the  Naval  Observatory  at  Washington  to  compute 
the  positions  of  the  sun,  moon,  and  many  of  the  stars  for 
some  years  in  advance.  Thus  navigators  sailing  on  long 
voyages  may  be  provided  with  the  means  of  making  rapid 
and  accurate  calculations  from  their  observations. 

If  we  could  imagine  ourselves  ignorant  of  where  we  are, 
of  the  day  of  the  year,  and  of  the  hour  of  the  day,  we  might 
be  able  to  realize  something  of  what  we  owe  to  man's  knowl- 
edge of  the  heavenly  bodies.  Calendars  and  timepieces  are 
made  and  corrected  with  reference  to  the  positions  of  the 
earth  and  the  sun  at  certain  times. 

At  least  once  every  day  the  correct  time,  as  determined 
by  the  position  of  the  sun  or  some  star,  is  telegraphed  from 
the  Naval  Observatory  to  every  city  in  the  country.  By 
electric  connections,  many  clocks  are  thus  set  right  once  a 
day.  The  calendar,  as  we  call  the  division  of  the  year  into 


THE  EARTH'S  PLACE  IN  THE  UNIVERSE  29 

months  and  days,  has  been  changed  twice  since  the  time  of 
Julius  Caesar.  These  changes  were  necessary  because  of 
the  neglect  of  a  few  seconds  in  calculating  the  length  of  a 
year.  If  the  calendar  had  not  been  corrected,  certain 
religious  festivals  would  by  this  time  be  observed  about  a 
month  later  by  the  calendar  than  the  seasons  in  which 
they  originally  occurred. 

20.  Longitude  and  Time.  —  The  meridians  of  longitude 
on  maps  and  globes  correspond  to  the  celestial  meridians; 
that  is,  the  meridian  of  longitude  of  a  given  place  lies  directly 
under  the  celestial  meridian  of  that  place.  For  example,  the 
meridian  of  90°  west  longitude  —  which  passes  through 
Memphis,  Tenn.,  Jackson,  Miss.,  and  New  Orleans,  La. — 
lies  on  the  earth  directly  under  the  celestial  meridian  of 
those  three  places.  The  meridian  passing  through  Green- 
wich, England,  has  been  adopted  by  all  countries  of  Europe 
and  the  Americas  as  the  prime  meridian,  or  the  meridian  of 
0°  longitude.  Places  within  180°  west  of  the  prime  meridian 
are  in  west  longitude;  places  within  180°  east  are  in  east 
longitude.  The  national  observatory  of  the  United  States, 
the  Naval  Observatory  at  Washington,  is  situated  77°  west 
of  the  prime  meridian,  —  therefore  at  77°  west  longitude. 
Delhi,  in  northern  India,  is  situated  about  77°  east  of 
Greenwich. 

When  the  sun  crosses  the  meridian  at  Washington,  it  is 
noon  there.  It  is  after  noon  at  places  east  of  Washington 
and  before  noon  at  places  to  the  west.  In  twenty-four  hours 
the  sun  will  again  be  overhead  at  Washington,  having 
(apparently)  passed  westward  around  the  earth  360°. 
In  each  hour,  then,  it  passes  over  15°.  When  it  is  noon 
at  Washington,  it  is  1  p.  m.  at  a  place  15°  east  of 
Washington,  and  11  a.  m.  at  a  place  15°  west  of  Washing- 
ton. If  15°  cause  a  difference  of  60  minutes  of  time, 
1  degree  will  cause  a  difference  of  4  minutes. 

News  of  an  event  which  occurred  at  1  p.  m.  in  Washington 


30        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

might  be  bulletined  by  telegraph  at  about  10  a.  m.  in  San 
Francisco  and  not  earlier  than  6  p.  m.  in  London. 

21.   Standard  Time.  —  It  is  evident  that  a  traveler  would 
find  his  timepiece  always  too  slow  or  too  fast  according  to 


FIG.  7. —  STANDARD  TIME  BELTS  IN  THE  UNITED  STATES 

The  meridians  of  75°,  90°,  105°,  120°  are  standard  time  meridians  for 
the  Eastern,  Central,  Mountain,  and  Pacific  time  belts  respectively.  If  the 
belts  were  of  uniform  width,  time  changes  would  be  made  at  meridians  half 
way  between  these  standard  meridians.  The  time  changes  are,  however, 
made  at  cities  which  are  important  railroad  centers.  The  lines  connecting 
these  cities  do  not  correspond  exactly  to  meridians. 

1.  What  is  the  widest  time  belt  in  the  United  States?  2.  What  is  the 
difference  between  sun  time  and  standard  time  at  places  on  the  70th  meridian? 
3.  On  the  115th?  4.  What  is  the  difference  between  sun  time  and  standard 
time  at  your  meridian?  5.  A  man  leaves  Washington  at  10  a.  m.  and  arrives 
at  Chicago  the  next  day  at  9  a.  m.  by  his  watch.  He  learns  that  the  next 
train  west  leaves  the  same  station  at  8: 10  a.  m.  Can  he  take  it?  Explain. 


which  way  he  journeyed,  if  each  city  regulated  its  time  by 
the  position  of  the  sun.  To  avoid  inconveniences  which 
would  occur  in  business,  and  in  railroad  and  steamboat  con- 
nections, the  United  States  government  in  1883  divided  the 
country  into  belts  about  15  degrees  wide.  Since  that  time, 


THE  EARTH'S  PLACE  IN  THE  UNIVERSE  31 

all  our  government  timepieces  in  any  one  belt  have  given 
the  same  time  at  any  moment.  When  the  government 
made  the  change  in  all  post-offices,  custom-houses,  and  naval 
stations,  people  had  to  make  the  same  change  for  their  own 
convenience,  and  now  Standard  Time  is  used  everywhere 
in  this  country.  A  similar  plan  of  time  belts  has  been 
adopted  in  Europe  also. 

Only  the  middle  of  a  belt  has  the  true  time  by  the  sun; 
other  parts  of  the  belt  differ  from  the  sun's  time  by  periods 
varying  from  one  to  thirty  minutes.  Most  people  do  not 
know  that  Standard  Time  is  not  the  same  as  sun  time. 

The  United  States  is  divided  into  four  time  belts,  called 
the  Eastern,  Central,  Mountain,  and  Pacific  belts.  Every- 
where in  a  given  belt  the  clocks  are  an  hour  ahead  of  those 
in  the  next  belt  west,  and  an  hour  behind  those  in  the  next 
belt  east.  When  it  is  noon  (Standard  Time)  at  New  York, 
it  is  11  a.  m.  in  Chicago,  10  a.  m.  in  Denver,  and  9  a.  m.  in 
San  Francisco.  It  is  then  5  p.  m.  in  London. 


EXERCISES 

1.  How  are  the  south,  east,  and  west  points  of  the  compass  deter- 
mined? 

2.  '(a)  How  many  degrees  from  the  equator  was  Commodore  Peary 
when  he  reached  the  north  pole?     (6)  How  many  degrees,  or  what  part 
of  a  circle,  was  the  distance  from  his  horizon  to  the  North  Star?     (c) 
How  many  degrees  above  the  north  point  on  the  horizon,  is  the  North 
Star  seen  at  the  place  where  you  live?     At  New  Orleans?     At  Sitka? 

3.  What  is  meant  by  the  earth's  period  of  rotation? 

4.  (a)  What  fraction  of  the  surface  of  the  earth  is  illuminated  by 
the  sun  at  one  time?     (6)   Why  does  the  lighted  space  move  to  the 
westward?     How  many  degrees  per  hour  does  it  move?     Why? 

5.  (a)  If  the  sun  rises  at  6  a.  m.  at   places  on  the  72d  meridian 
W.  longitude,  at  what  meridian  will  it  rise  an  hour  later?     (6)  At  what 
longitude  will  the  sun  be  setting  when  it  is  rising  on  the  90th  meridian 
W.  longitude? 

6.  How  many  degrees  north  of  the  equator  is  the  sun  when  it  is 
visible  for  twenty-four  hours  at  70°  N.  latitude? 


32        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

7.  Explain  the  location  of  the  tropic  of  Capricorn  and  the  antarc- 
tic circle. 

8.  In  what  month  of  the  year  is  it  midsummer  and  continuous 
daylight  at  the  south  pole? 

9.  In  what  direction  do  windows  of  a  house  face,  if  the  sun  shines 
directly  into  them  at  noon  in  the  United  States?     In  Cape  Colony, 
Africa?    Why? 

10.  Which  is  the  drier  and  warmer  sidewalk  in  winter,  that  on  the 
north  or  on  the  south  side  of  a  city  street?     Why? 

11.  At  what  season  does  the  sun  cast  the  longest  shadows  at  noon 
in  New  England?     In  what  direction  do  they  lie?     Name  a  country 
where,  in  both  respects,  the  opposite  is  true  for  the  same  season. 


.  CHAPTER  II 

THE    EARTH'S    NEAREST    NEIGHBORS:     THE    MOON    AND 
THE    PLANETS 

22.  The  Earth,  a  Planet.  —  It  has  been  known  for  five 
hundred  years  that  the  earth  moves  around  the  sun  once  in 
about  365  days.     It  has  since  been  learned  that  the  earth 
is  nearly  spherical;  that  its  orbit  is  nearly  a  circle;   that  it 
is  kept  in  place  by  an  attracting  force,  called  gravitation; 
and  that  there  could  be  no  life  on  the  earth  if  it  were  not 
for  the  light  and  heat  which  it  receives  from  the  sun.     Be- 
sides the    earth,   there   are   seven  other   bodies  of   which 
nearly  all   these  facts   are  true.     These  bodies  are  called 
planets. 

23.  The    Motion    of    the    Planets.  —  The  star  Regulus 
changes  its  position  in  the  sky,  but  it  is  always  at  the  end 
of  the  handle  of  the  sickle  in  Leo.     Similar  statements  may 
be  made  of  all  the  stars  we  have  studied.     They  do  not 
change  their  position  with  relation  to  other  stars.     Among 
the  stars,  however,  are  seen  a  few  bright  bodies  that  shine 
with  a  steadier  light  and  do  not  keep  .the  same  places  in 
the   constellations.     At  the  end  of  a  month,  for  instance, 
we  may  see  that  they  have  moved  away  from  or  nearer  to 
aome  star  in  the  same  part  of  the  sky.     These  are  the  planets 
(from  a  Greek  word  meaning  "wanderer").     The  brightest 
of  the  planets  are  Venus,  Jupiter,  Mars,  and  Saturn.     It 
is  very  seldom  that  all  four  are  seen  at  the  same  time  in 
any  evening,  but  two  are  often  in  the  sky  together,  and 
sometimes    three.      The    three    other    planets  —  Mercury, 
Uranus,   and  Neptune  —  cannot   be   seen   well   without  a 
telescope. 

33 


34        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

If  we  could  stand  upon  Venus  and  observe  the  earth,  we 
should  see  that  the  earth  changes  its  position  with  relation 
to  the  stars,  just  as  the  other  planets  do. 

24.  The  Revolution  of  the  Planets.'— The  other  planets, 
like  the  earth,  revolve  around  the  sun,  but  not  in  the  same 


FIG.  8. --SIMON  NEWCOMB:  ASTRONOMER.     1835-1909 

With  his  appointment  to  the  United  States  Naval  Observatory  in  1861, 
his  greater  life  work  began.  .  .  .  The  sun  and  the  moon  and  the  planets  yielded 
their  secrets  to  the  call  of  his  mighty  intellect,  and  science  has  profited  to 
the  benefit  of  humanity  in  consequence  of  the  life  of  Simon  Newcomb.  .  .  . 
They  buried  him  in  Arlington,  where  only  those  who  have  served  their 
country  are  permitted  to  lie. — MARCUS  BENJAMIN,  in  Leading  American 
Men  of  Science. 

period  that  the  earth  does.  The  earth's  period  of  revolution 
is  about  365  days,  called  one  year  or  twelve  months.  That 
of  Venus  is  seven  and  one-half  months,  of  Mars  one  year 
and  ten  months,  of  Jupiter  about  twelve  years,  of  Saturn 
nearly  thirty  years.  The  orbits  are  all  nearly  circular,  like 


THE  EARTH'S  NEAREST  NEIGHBORS 


35 


Neptune 


FIG.  9. — RELATIVE  DISTANCES  OF  SOME  OF  THE  PLANETS 

1.  Which  of  these  planets  comes  nearest  to  the  earth?  2.  How  far 
away  is  Jupiter  when  it  is  nearest  to  the  earth?  3.  Light  passes  from  the  sun 
to  the  earth  in  about  eight  minutes.  How  many  hours  does  it  take  to  reach 
Neptune? 

the  earth's,  and  they  lie  one  outside  another,  with  the  sun 
almost  at  the  center. 

Planets  are  never  seen  in  the  northern  part  of  the  sky,  but 
are  always  in  the  same  belt  from  east  to  west  in  which  the 
sun  and  moon  are  seen.  If  all  the  planets  revolved  about 


36        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

the  sun  in  the  same  period,  each  planet  would  always  be 
seen  in  the  same  place,  with  relation  to  the  others;  but 
when  the  earth  has  gone  around  the  sun  once,  Venus  has 
gone  about  one  and  two-thirds  times  around,  while  Mars 
has  gone  about  half-way  around. 

25.  Why   the   Planets   Shine.  —  The  stars  shine  because 
they   are   white-hot,  but   the   planets   are    bright   because 
the     sun's     light    falls    on    them    and    a    part    of    it    is 
reflected   to   us.     A  mirror  can  be  made  to  reflect  nearly 
all  the  light  that  falls  upon   it.      The   planets,    however, 
reflect   only  about   half   the  light  they   receive    from   the 
sun.     If  the  earth  were  seen  from  one  of  the  planets,  it 
would  probably  appear  very  nearly  as  bright  as  the  planets 
look  to  us. 

26.  The  Size  of  the  Planets  and  their  Distances  from 
the  Sun.  —  Venus  is  nearly  as  large  as  the  earth ;    Mars  is 
smaller  than  the  earth;   Saturn  is  many  times  as  large;   and 
Jupiter  is  as  large  as  all  the  others  put  together.     Mercury 
is  much  smaller  than  the  earth,  and  Uranus  and  Neptune 
are  about  four  times  as  large  as  the  earth. 

The  distances  of  the  planets  from  the  sun  differ  greatly. 
The  smallest  planets  are  nearest  to  the  sun.  We  know  the 
earth  to  be  nearly  93,000,000  miles  from  the  sun.  Mercury 
is  .4  of  that  distance  from  the  sun  and  Venus  .7.  Mars  is 
1.5  times  as  far  away;  and  Jupiter  is  5,  Saturn  9,  Uranus 
19,  and  Neptune  30  times  as  far  from  the  sun  as  the  earth 
is.  Mercury  is  so  near  the  sun  that  it  is  usually  in  the  sky 
in  the  daytime.  Uranus  and  Neptune,  because  of  their 
great  distance,  seem  like  stars  of  the  sixth  and  ninth 
magnitude  respectively.  (LABORATORY  MANUAL,  Exercise 

in.) 

27.  Venus.  —  Venus  is  so  like  the  earth  in  size  and  dis- 
tance from  the  sun  that  it  is  sometimes  called  the  earth's 
twin  planet.     No  one  can  tell  whether  it  has  continents  and 
oceans,  mountains  and  plains.     Its  surface  cannot  be  clearly 


THE  EARTH'S  NEAREST  NEIGHBORS       37 

seen  because  of  its  cloud-like  atmosphere.  This  atmosphere 
reflects  a  great  deal  of  the  sun's  light,  and  consequently 
Venus  is  the  brightest  planet. 

28.  Mars.  —  Mars  has  been  much  studied  and  some  as- 
tronomers think  that  light  and  dark  markings  upon  its  surface 
indicate  the  presence  of  land  and  water  like  the  earth's; 
that  the  land  is  desert  at  some  seasons  and  covered  with 
vegetation  at  others;    and  that  around  the  poles  there  are 
snow  and  ice  which  change  in  amount  with  the  seasons. 
The  seasons  differ  very  much  as  ours  do.     Mars  receives  less 
than  half  as  much  light  and  heat  as  the  earth,  because  of  its 
greater  distance  from  the  sun,  so  that  if  there  is  life  on  Mars, 
it  cannot  be  the  same  kind  of  life  as  on  the  earth.     Mars  has 
two  moons  or  satellites,  so  small  that  they  cannot  be  seen 
except  through  the  largest  telescopes. 

29.  Jupiter.  —  Jupiter  is  the  giant  planet,  and  if  it  were 
as  near  to  us  as  the  moon  is,  it  would  seem  forty  times  as 
wide  as  the  moon  does.     Jupiter  has  four  moons  as  large  as 
our  moon,  and  five  very  small  ones.     Galileo,  an  Italian 
astronomer,  discovered  the   four  larger  ones  in   1610,  the 
first  time  he   looked  at  Jupiter  with   a  telescope.     They 
were    the    first    heavenly    bodies     discovered.      The    five 
smaller   satellites   have   been   discovered,    one    at   a   time, 
since   1892.     Four  of  them  were  discovered  by  means  of 
photography.     Heavenly  bodies  whose 'light  is  too  faint  to 
make  an  impression  upon  the  eye,  even  through  a  telescope, 
can  be  photographed  with  a  telescope-camera.     By  exposing 
the  plate  a  long  time  —  sometimes  for  many  hours  —  it  is 
possible  to  get  an  impression  from  the  faint  light  of  these 
distant  bodies. 

30.  Saturn.  —  Saturn,  as  seen  through  the  telescope,  is 
a  wonderful  sight,  because  of  the  bright,  thin,  flat  rings  which 
revolve  about  the  planet  without  touching  it.     When  Saturn 
is  situated  so  as  to  show  the  broad  side  of  the  rings  (as  it  is 
once  in  fifteen  years),  it  is  much  brighter  than  when  we 


38        FIRST  YEAR  COURSE   IN   GENERAL  SCIENCE 


see  only  the  thin   edges  of    the  rings.       Saturn    has    ten 
moons,  some  of  which  are  very  small. 

31.  The    Moon.  —  Except    the   sun,    the    moon    is    the 
most  important  to  the  earth  of  all  the  heavenly  bodies.     It  is 

our  nearest  neighbor,  being  less  than  a 
quarter  of  a  million  miles  away.  It  is 
so  familiar  a  sight  that,  except  at  the 
time  of  new  or  full  moon,  we  scarcely 
remark  upon  it.  The  moon  is  the  only 
satellite  of  the  earth.  Its  diameter  is 
about  2,000  miles,  one  quarter  of  the 
earth's  diameter.  No  other  planet  has 
1914  a  satellite  so  large  in  proportion  to  its 
own  size. 

Like  the  satellites  of  the  other 
planets,  the  moon  revolves  in  a  nearly 
circular  orbit.  It  takes  almost  twenty- 
eight  days  to  go  once  around  the  earth 
and  therefore  makes  about  thirteen 
revolutions  a  year.  While  the  moon 
makes  one  journey  around  its  orbit,  it 
rotates  only  once  upon  its  axis.  Because 
the  moon's  period  of  revolution  is  the  same  as  its  period  of 
rotation,  it  always  turns  the  same  side  toward  the  earth. 
As  the  diagram  shows  (Fig.  11),  when  the  moon  has  gone  one 
quarter  of  the  distance  around  the  earth,  it  has  turned  upon 
its  axis  one  quarter  of  the  way.  Thus,  though  each  portion 
of  the  moon  is  in  a  different  position  with  relation  to  the 
sun,  the  same  side  of  the  moon  is  always  turned  toward 
the  earth,  around  which  it  is  revolving.  No  one  ever  saw 
the  other  side  of  the  moon. 

32.  Changes   in   the   Apparent  Form   of   the   Moon.  — 
The  moon,  like  the  planets  and  the  other  satellites,  is  nearly 
spherical  in  form,  but  it  does  not  always  appear  so.     At 
some  times  it  looks  like  a  disk  and  at  others  a  half-disk,  and 


1907 


1909 


1911 


1913 


FIG.  10.  —  SATURN 
1.  From  which  posi- 
tion of  Saturn  should 
we  receive  the  most 
light?  Why?  2.  How 
many  years  are  there 
between  the  brightest 
and  the  least  bright 
appearances  of  Saturn? 
3.  Does  its  brightness 
change  suddenly? 


THE  EARTH'S  NEAREST  NEIGHBORS  39 

sometimes  it  is  crescent-shaped.  At  certain  times  it  is 
invisible.  When  it  is  on  the  other  side  of  the  earth  from 
where  we  are,  of  course  we  do  not  see  it. 

The  moon's  light  is  reflected  sunlight,  and  the  sun  shines 
upon  half  of  the  moon  all  the  time,  except  during  a  lunar 
eclipse,  that  is,  an  eclipse  of  the  moon.  When  the  moon 
is  in  the  same  direction  from  us  as  the  sun,  the  sun's  light 
falls  upon  the  half  of  the  moon  turned  away  from  us,  and 
the  side  toward  us  is  dark  and  hence  invisible. 


Moon 


FIG.  11. — ROTATION  AND  REVOLUTION  OF  THE  MOON 

1.  What  quarters  of  the  moon  are  turned  toward  the  earth  in  position 
1  shown  at  the  left  side  of  the  diagram?  2.  What  quarters  are  lighted? 
Why?  3.  What  part  of  the  moon's  revolution  is  .completed  between  posi- 
tions 1  and  2  (at  the  bottom)?  4.  What  part  of  its  rotation?  5.  Name  the 
quarters  of  the  moon  turned  toward  the  earth  in  position  2.  6.  Are  they 
both  lighted?  Why? 

In  a  day  or  two,  as  the  moon  changes  its  direction  from 
us  with  relation  to  the  sun,  light  strikes  a  small  part  of  the 
half  turned  toward  us  and  gives  the  crescent  or  "new 
moon,"  seen  in  the  western  sky  soon  after  sunset.  As  the 
moon  continues  to  move  eastward  around  the  earth,  it  is 
seen  farther  from  the  western  horizon  each  evening,  a  larger 
portion  of  the  half  toward  us  is  lighted,  and  the  crescent 
changes  gradually  to  a  half -disk.  This  is  called  "first  quar- 


40        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

ter,"  because  one  fourth  of  the  time  from  new  moon  to  the 
next  new  moon  has  passed. 

As  the  days  go  on,  the  half-disk  grows  to  a  whole  disk  or 
full  moon,  and  this  in  another  week  has  diminished  to  a 
half-disk  called  "  third  quarter."  In  about  a  week  a  small 
crescent,  the  "old  moon,"  is  seen  in  the  east  before  sunrise. 
Then  for  a  day  or  two  the  moon  is  again  invisible  because  it 
is  in  the  same  direction  as  the  sun.  When  next  seen,  it  is 
a  slender  crescent  in  the  western  sky. 

The  time  from  new  moon  to  the  next  new  moon  is  about 
twenty-nine  days.  This  was  the  period  which  the  American 
Indians  used  in  reckoning  time  by  "moons." 

33.  The    Time    of    Moonrise.  —  The  moon  rises,  on  the 
average,  about  fifty  minutes  later  each  day  than  the  day 
before.     It  has  moved  eastward  from  the  place  where  it  was 
twenty-four  hours  before,  and  therefore  the  earth  must  turn 
a  little  farther  on  its  axis  before  the  moon  is  visible  at  the 
horizon.     The  full  moon  rises  at  the  time  of  sunset,  and 
about  two  weeks  later  the  new  moon  rises  at  sunrise  but 
is  invisible  to   us.      In   a   day   or  two,   as  it  has   moved 
eastward,  it   rises  an   hour  or   so   after   sunrise,  but  it  is 
generally  invisible  to  us  while  the  sun  is  shining.     People 
rarely   speak    of    the    rising   of    the   new   moon,    although 
it  actually  rises  at  about  the  same  time  and  place  that  the 
sun  does. 

34.  The    Moon's    Surface.  —  Looking  at  the  moon  with 
the  naked  eye,  we  notice  that  some  portions  are  less  bright 
than  others.     With  the  telescope  it  is  found   that   these 
darker  portions  are  nearly  level  surfaces  like  plains.     Around 
them  are  brighter  elevations  or  mountains,  some  of  which 
look  like  extinct  volcanoes.     In  the  summits  of  some  of  these 
mountains  there  are  deep  depressions  or  craters  with  smaller 
peaks  in  them.      There  is  no  air  or  water  on  the  moon,  so 
far    as  men    have   been    able   to    learn    by   any  scientific 
methods.     No  changes  of  importance  have  been  observed 


THE  EARTH'S  NEAREST  NEIGHBORS  41 


FIG.  12. —  A  PHOTOGRAPH  OP  THE  MOON 

This  photograph  was  made  about  10  days  after  new  moon.  One  half  of 
the  moon  is  lighted,  as  it  is  always.  1.  How  much  of  the  lighted  half  is 
visible  in  the  picture?  2.  The  diameter  of  the  moon  is  about  2,000  miles; 
estimate  the  width  of  the  elliptical  plain  on  the  right.  3.  How  wide  is  the 
largest  ring-shaped  elevation  that  you  can  see? 


42       FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 

since  Galileo  looked  at  the  moon  with  his  first  telescope 
more  than  three  hundred  years  ago. 

35.  Eclipses    of    the    Sun.  —  As  the  light  from  the  sun 
cannot  pass  through  the  moon,  there  is  always  a  dark  space 
or  shadow  stretching  away  from  the  moon  on  the  side  oppo- 
site the  sun.     When  the  moon  comes  directly  between  the 
sun  and    the    earth,   this    shadow   sometimes    reaches  the 
earth  and  a  solar  eclipse  occurs. 

As  the  moon  is  a  sphere,  the  shadow  is  cone-shaped,  and 
where  it  touches  the  earth,  it  makes  a  round  or  an  oval 
shadow  spot,  just  as  a  cloud  between  the  earth  and  the  sun 
casts  a  shadow  on  the  ground.  The  shadow  is  less  than  170 
miles  in  diameter  where  it  falls  upon  the  earth.  The  sun  is 
completely  hidden  from  people  who  are  on  the  part  of  the 
earth  where  the  shadow  falls. 

When  a  total  eclipse  of  the  sun  occurs,  darkness  comes 
on  suddenly,  for  the  daylight  lasts  as  long  as  even  a  small 
portion  of  the  sun  is  visible.  When  the  last  crescent  of  the 
sun  has  disappeared,  it  is  as  dark  as  night  and  stars  are 
visible. 

The  outside  gaseous  portion  of  the  sun,  the  corona,  is 
never  seen  except  at  a  solar  eclipse,  because  its  light  is  so 
much  fainter  than  the  light  of  the  rest  of  the  sun.  During 
a  total  solar  eclipse,  the  corona  shines  out  around  the  dark 
moon  with  a  beautiful,  soft,  pearly  light,  sometimes  tinted 
pale  green  or  rose  color. 

36.  Eclipses  of  the  Moon.  —  In  a  lunar  eclipse  the  earth 
is  between  the  sun  and  the  moon.    The  shadow  is  then  cast 
by  the  earth  and  it  is  much  larger  than  the  shadow  made  by 
the  moon  in  a  solar  eclipse.     Instead  of  making  a  dark  spot 
upon   the  moon,  it  may  cover   the  whole  moon.     As  the 
moon  enters  the  shadow  space,  a  portion  of  the  moon  is 
darkened  while  the  rest  of  the  moon  is  as  bright  as  usual. 
At  this  time  the  form  of  the  earth  is  shown  in  the  curved 
edge  of  the  shadow.     We  "see  our  own  shadow."     In  a 


THE    EARTH'S    NEAREST    NEIGHBORS 


43 


total  lunar  eclipse  the  moon  is  in  the  shadow  more  than  an 
hour,  while  in  a  solar  eclipse  the  sun  is  hidden  only  a  few 
minutes  at  the  longest. 

Eclipses  of  the  moon  are  much  more  frequently  seen  than 
solar  eclipses.  The  moon  is  visible  to  people  on  half  the 
earth  at  one  time,  so  when  a  lunar  eclipse  occurs,  many  of 
the  earth's  inhabitants  may  see  it.  In  a  solar  eclipse,  how- 
ever, the  shadow  spot  covers  only  a  small  portion  of  the 
earth  and  a  solar  eclipse  is  visible  only  to  those  within  this 
small  area. 

Astronomers  can  predict  with  great  exactness  the  times  at 


FIG.  13.  —  LUNAR  AND  SOLAR  ECLIPSES 

1.  Compare  the  shadows  cast  by  the  earth  and  the  moon.  2.  Why  is 
there  this  difference?  3.  From  what  portion  of  the  earth,  as  shown  in  this 
figure,  is  the  lunar  eclipse  visible?  4.  The  solar  eclipse?  5.  In  which  of 
these  portions  do  the  larger  number  of  people  live? 

which  eclipses  will  occur,  and  almanacs  give  the  dates  of 
eclipses  for  the  current  year. 

37.  Telescopes.  —  There  are  two  reasons  why  a  telescope 
enables  one  to  see  an  object  better  than  is  possible  with  the 
unaided  eye.  The  light  which  makes  a  body  visible  is  re- 
ceived through  a  small  opening  in  the  front  of  the  eye, 
called  the  pupil.  When  the  eye  is  placed  at  the  eyepiece  of 
a  telescope,  it  receives  all  the  light  that  falls  upon  a  lens, 
some  inches  in  diameter,  at  the  other  end  of  the  telescope. 
Thus  more  light  than  usual  is  brought  to  the  eye  and  the 


44       FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


FIG.  14.  —  THE  LUNAR  SHADOW 


THE  EARTH'S  NEAREST  NEIGHBORS       45 

image  is  brighter.     Secondly,  by  its  form  the  lens  directs  the 
light  in  such  a  way  that  the  image  is  magnified. 

The  largest  lenses  used  in  telescopes  in  this  country  are  the 
lens  forty  inches  in  diameter  in  the  Yerkes  telescope  of  the 
University  of  Chicago,  and  one  of  thirty-six  inches  in 
the  Lick  telescope  of  the  University  of  California.  Many 
colleges  have  telescopes  with  lenses  from  eight  to  twenty 
inches  in  diameter,  and  the  great  universities  and  national 
observatories  have  much  larger  ones.  The  largest  telescope 
in  the  United  States  Naval  Observatory  at  Washington  has 
a  twenty-six-inch  lens. 

Questions  on  Fig.  14.  1.  What  kind  of  eclipse  does  this  picture  represent? 
2.  Considering  only  the  motion  of  the  moon  around  the  earth,  in  which 
direction  would  the  shadow  spot  on  the  earth  travel?  3.  Does  it  travel 
more  or  less  rapidly  because  the  earth  moves  in  the  same  direction?  4.  If 
the  moon  were  fixed  and  the  earth  rotated,  as  it  does,  in  what  direction 
would  the  shadow  spot  move? 

EXERCISES 

1.  How  may  any  observer  distinguish  the  planets  from  stars? 
Could  it  be  done  in  one  observation?     Why? 

2.  Which  is  more  like  a  mirror,  the  surface  of  land  or  of  water? 
Does  the  planet  earth,  then,  reflect  much  or  little  light? 

3.  Why  is  it  more  reasonable  to  talk  of  the  possibility  of  life  upon 
Mars  than  upon  any  other  planet? 

4.  Which  receives  more  light  and  heat  from  the  sun,  Mars  or  the 
earth?     Give  the  reason. 

5.  How  many  rotations  does  the  earth  make  while  the  moon  is 
making  one? 

6.  What  portion  of  the  moon  is  lighted  by  the  sun  at  one  time? 
From  what  body  does  the  moon  receive  light  upon  one  half  only? 

7.  Why  does  the  moon  have  day  and  night?     How  long  does  day- 
light last  at  any  one  place  on  the  moon? 

8.  In  what  direction  is  the  full  moon  seen  at  sunset? 

9.  In  what  part  of  the  sky,  and  at  what  time  of  the  day,  is  the 
new  moon  first  visible?     What  is  its  form? 

10.   Why  is  not  the  moon  visible  from  the  earth  at  the  time  of  a 
solar  eclipse? 


CHAPTER  III 
MATTER    AND    ITS   PROPERTIES 

38.  The    Study    of    Science.  —  By  constant  observation 
and  experiment,  men  have  learned  much  about  the  earth 
on  which  we  live.     What  they  have  learned  has  enabled 
them  to  do  many  things  which  would  have  seemed  wonder- 
ful to  people   who    lived    even   one   hundred    years    ago. 
In     order    to    understand    the    work    going   on    about    us 
and  the  effects  of  changes  that  have  occurred  in  the  earth 
and  are  still  occurring,  it  is  necessary  to  study  the  ele- 
ments of  science  which  men  have  learned  in  the  centuries 
preceding. 

39.  Matter.  —  The  heavenly  bodies  are  so  distant  that 
we  can  use  only  the  sense  of  sight  in  studying  them;   but  to 
find  out  all  that  we  can  about  things  near  at  hand,  we  may 
use  all   our    senses.     We  not   only   look  at   these   things, 
but  we  may  handle  them,  or  smell  of  them,  sometimes  taste 
of  them,  or  listen  for  sounds  they  may  make.     The  name 
matter  has  been  given  to  everything  that  takes  up  room  and 
has. weight.     We  learn  about  matter  by  use  of  the  senses. 
The  earth,  the  sun,  bone,  wood,  brick,  water,  and  air  are  all 
made  up  of  matter. 

There  are  two  classes  of  matter,  living  and  non-living. 
Ability  to  move  of  itself  and  to  grow  distinguishes  living 
matter  from  non-living  matter. 

Matter  is  believed  to  be  composed  of  minute,  invisible 
particles  called  molecules.  No  one  knows  much  about 
molecules,  but  some  facts  are  best  explained  by  believing 
that  these  invisible  particles  exist  and  that  they  are  always 

46 


MATTER  AND  ITS  PROPERTIES  47 

vibrating  —  that  is,  moving  back  and  forth  in  their  places 
—  with  great  rapidity. 

40.  The    Divisions    of    Matter.  —  Any  separate  portion 
of  matter  is  called  a  body.     A  molecule,  a  book,  a  pebble, 
a  boulder,  a  star,  a  fish,  a  tree  are  bodies. 

A  particular  kind  of  matter  is  called  a  substance.  Iron, 
sugar,  salt,  water,  wood  are  substances  of  which  bodies  are 
made. 

If  the  molecules  of  a  substance  are  all  of  one  kind  of  mat- 
ter, that  substance  is  called  an  element.  Iron  is  an  element, 
and  nothing  but  iron  has  ever  been  made  from  iron  alone. 
Gold  and  silver  are  elements. 

41.  Some    Important    Elements.  —  Of  the  eighty  known 
elements,  only  about  one  half  are  of  much  importance  at 
present.     The  elements  most  abundant  in  the  sun  and  in 
the  land  upon  which  we  live,  in  the  air  and  water  surrounding 
it,  and  in  the  bodies  of  plants  and  animals  are : 

Certain  solid  metals:  aluminum,  calcium,  copper,  gold, 
iron,  lead,  nickel,  platinum,  potassium,  silver,  sodium. 

One  liquid  metal :  mercury. 

Certain  solids  which  are  not  metals:  arsenic,  carbon, 
iodine,  phosphorus,  silicon,  sulphur. 

Certain  gases:   chlorine,  hydrogen,  nitrogen,  oxygen. 

These  elements  very  seldom  exist  by  themselves  in  the  land, 
or  in  the  water,  or  in  our  bodies.  They  are  united  with  each 
other,  forming  another  class  of  substances,  called  compounds. 

42.  Compounds.  —  If  we  heat  a  little  of  the  element  mer- 
cury (a  heavy  silvery  liquid)  and  drop  into  it  the  right  quan- 
tity of  the  element  iodine  (a  bluish-black  scaly  solid),  neither 
color  remains.     A  new  substance  appears,  not  liquid  like 
mercury,  not  in  flat  scales  like  iodine,  but  in  the  form  of  red 
powder.     This  is  mercury  iodide,  a  compound  of  mercury 
and  iodine. 

A  compound  is  a  substance  made  up  of  two  or  more  ele- 
ments combined  in  definite  proportions  by  weight,  and 


48        FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 

having  characteristics  different  from  those  of  the  elements 
which  compose  it.  Sugar,  salt,  and  water  are  compounds. 

Considering  that  the  eighty  known  elements  may  be  com- 
bined in  groups  of  two  or  more,  and  in  different  proportions, 
it  is  evident  that  many  thousands  of  compounds  may  be 
formed  from  them. 

If  two  elements,  as  mercury  and  iodine,  unite  to  form  a 
new  and  different  substance,  or  if  a  substance  separates  into 
the  parts  of  which  it  is  composed  and  two  or  more  elements 
result,  such  a  change  is  a  chemical  change.  No  one  of  the 
resulting  parts  is  like  the  original. 

43.  Mixtures.  —  Nearly  everything  that  we  eat  or  drink, 
the  air  we  breathe,  the  substances  of  which  our  bodies  are 
made,   the   paper   and   ink  with   which   we   write,  —  each 
of  these  things  is  either  a  compound  or  a  mixture.     With  the 
exception   of   carbon,  sulphur,  and   the   metals,  we  rarely 
see   or   use   anything   that  is  an  element.     A  mixture  is 
formed  when  two  or  more  substances    (elements   or   com- 
pounds)   are  brought   so   closely  together  as  to  seem  one 
substance  and  yet  retain  their  original  qualities.     Sirup  is  a 
mixture  of  sugar  and  water;   it  is  still  sweet  and  a  liquid. 
Air  is  a   mixture   of   nitrogen,    oxygen,    and    other   gases; 
tincture  of  iodine  is  a  mixture  of  alcohol  and  iodine;  brine 
is  a  mixture  of  salt  and  water.     It  is  often  difficult  for  any 
one  but  a  chemist  to  distinguish   between   mixtures  and 
compounds. 

The  dissolving  of  salt  or  sugar  in  water  is  an  example  of 
a  physical  change  because  no  new  substance  is  formed.  The 
resulting  substance  is  liquid,  as  water  is.  It  has  a  salt  or  a 
sweet  taste,  as  salt  or  sugar  has.  Each  substance  could  be 
recognized  by  a  description  of  the  mixture.  The  same  salt 
or  sugar  could  be  procured  in  the  solid  form  by  allowing 
the  water  to  evaporate. 

44.  Properties.  —  The   word  property,  as  it  is   used   in 
science,  means  a  quality  or  characteristic  possessed  by  a 


MATTER  AND  ITS  PROPERTIES  49 

kind  of  matter.  Hardness  is  a  property  of  rock;  magnetism 
is  a  property  of  iron;  red  color  is  a  property  of  blood.  To 
name  the  properties  of  a  substance  is  to  describe  it.  For 
example,  water  is  a  colorless,  transparent  liquid. 

There  are  three  properties  which  are  possessed  by  all 
matter,  living  and  non-living, — 'elements,  compounds,  and 
mixtures.  These  properties  are  extension,  weight,  and 
inertia. 

45.  Extension.  —  Every  body  has  extension  in  three  di- 
rections, i.e.,  it  has  length,  width,  and  thickness  or  depth. 
Examples:    a  block,  a  pencil,  a  ball.     The  space  which  a 
body  occupies  is  called  its  volume.     A  body  8  in.  long,  3  in. 
wide,  and  2  in.  thick  occupies  48  cu.  in.  of  space,  or  has  a 
volume  of  48  cu.  in. 

A  straight  line  drawn  on  a  sheet  of  paper  represents  exten- 
sion in  one  direction  only,  and  a  surface  marked  off  on  a 
table-top  has  extension  in  two  directions  only;  therefore,  the 
line  and  the  surface  are  not  bodies. 

46.  Systems    of   Measures.  —  The  units  used  in  measur- 
ing extension  by  the  British  system  of  measures  (the  inch, 
foot,  yard,  rod,  and  mile)  have  no  common  relation  to  each 
other.     An  inch  is  one  twelfth  of  a  foot;  a  foot  is  one  third  of 
a  yard;   and  the  relation  of  the  foot  or  the  yard  to  the  rod 
involves  a  complex  fraction.     In  the  French  or  metric  sys- 
tem, every  unit  of  length  is  one  tenth  of  the  next  higher,  or 
ten  times  the  next  lower  denomination. 

So  much  time  can  be  saved  in  computation  by  the  metric 
system  that  the  United  States  government  has  authorized 
its  use  in  government  work.  In  most  colleges  and  many 
manufactories,  scientific  measurements  are  made  in  metric 
units.  It  is  hoped  that  in  time  the  metric  system  will  come 
into  general  use  in  the  United  States,  as  it  has  now  in  most 
countries  of  Europe. 

The  decimal  system  of  money  was  adopted  in  the  United 
States  more  than  a  century  ago,  and  some  of  its  denomi- 


50        FIRST  YEAR  COURSE   IN   GENERAL  SCIENCE 

nations   will   help   us   in    remembering    the    units    of    the 
metric  system. 

10  mills  make  1  cent. 

10  cents  make  1  dime., 

10  dimes  make  1  dollar. 

We  use  the  dollar  as  our  unit  and  regard  the  smaller  divi- 
sions as  fractions  which  can  always  be  expressed  decimally. 
It  is  not  necessary  to  write  the  names  of  the  parts,  for  the 
dimes,  cents,  and  mills  are  expressed  decimally. 


I 

cm. 


Inches 


FIG.  15.  —  ENGLISH  AND  METRIC  MEASURE 

1.  What  is  the  equivalent  of  1  in.  in  centimeters?  2.  How  many 
millimeters  in  1  in.?  3.  From  the  answer  to  1,  find  which  is  longer,  a 
yard  or  a  meter. 

47.  Measurement  of  Extension.  —  In  measuring  length 
by  the  metric  system,  the  meter  is  the  unit.  Its  divisions 
are  thus  expressed: 

10  millimeters  (mm.)  make  1  centimeter  (cm.). 

10  centimeters  make  1  decimeter  (dm.). 

10  decimeters  make  1  meter  (m.). 

10  meters  make  1  dekameter  (Dm.). 

10  dekameters  make  1  hectometer  (Hm.). 

10  hectometers  make  1  kilometer  (Km.). 

The  prefixes  square  and  cubic  are  used  in  measures  of  sur- 
face and  volume  respectively.  A  block  measuring  5  centi- 
meters on  each  edge  has  on  each  side  a  surface  of  25  square 
centimeters,  and  contains  125  cubic  centimeters. 

The  number  of  meters  is  more  commonly  written  than 
the  words  dekameter  and  hectometer,  but  the  kilometer  (one 


MATTER  AND  ITS  PROPERTIES 


51 


FIG.  16.  —  MEASURES  OF 
VOLUME 


thousand  meters)  is  the  unit  used  in  measuring  distances. 
A  meter  is  about  3J  feet;  a  kilometer  is  about  f  of  a  mile. 
Instead  of  describing  a  river  as  1  dekameter  deep,  3  hec- 
tometers wide,  and  125  kilometers  long,  we  should  say  it  was 
10  meters  deep,  300  meters  wide, 
and  125  kilometers  long. 

48.  Weight.  —  When  we  have 
found  out  the  volume  of  a  body, 
we  still  do  not  know  how  much 
matter  there  is  in  it.    The  way  to 
find  out  is  to  weigh  it,  and  the 
amount  of  matter  is  called  weight. 
Two  bodies  of  the  same  volume 
may  differ  greatly  in  weight;  as, 

a  Cubic  foot  of  lead    and   a  cubic  I.  How  many  cm.  in  1  dm.? 

foot  Of  COrk,  a  quart  of  kerosene     2-  ?ow  many  sq.  cm.  in  a  surface 

1    dm.    on  each   edge?     3.  How 

and  a  quart  of  mercury,  a  cubic    many  cu.  cm.  in  a  block  10  cm. 
centimeter   of  ice  and   a   cubic    ?n  each  edge?u  4-  What  name 

is  given  to  such  a  volume: 

centimeter  of  stone. 

49.  Measurement  of   Weight. — The  gram   (about  -fa  of 
an  ounce  or  fifteen  grains)  is  the  metric  unit  for  small  weights; 
it  is  used  by  druggists,  chemists,  and  dealers  in  gems  and 
precious  metals,  and  in  all  scientific  work.     The  table  of 
weights  is  similar  to  that  of  length,  except  that  the  unit  is 
the  gram.     A  kilogram  (one  thousand  grams)  is  equivalent 
to  about  2j  pounds;   it  is  the  unit  used  in  measuring  large 
masses. 

The  weight  of  one  cubic  centimeter  of  pure  water  at  the 
temperature  of  39°  Fahrenheit  is  accepted  as  the  unit  of 
weight,  one  gram  (g.) ;  and  it  is  nearly  correct  to  assume  that 
one  cubic  centimeter  of  clean,  cold  water  weighs  a  gram. 
Therefore  one  thousand  cubic  centimeters  of  water  weigh 
one  thousand  grams  or  a  kilogram  (kg.).  It  is  a  simple 
matter  to  determine  the  weight  of  water  in  a  tank  or  reservoir 
by  measuring  the  capacity  of  the  tank  in  cubic  centimeters. 


52        FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 


If  a  tank  is  50  cm.  x  40  cm.  X  30  cm.,  its  capacity  is  60,000 
cu.  cm.,  and  the  weight  of  water  contained  in  the, tank,  when 
full,  is  60,000  grams  or  60  kilograms.  If  the  liquid  were 
twice  as  heavy  as  water,  its  weight 
would  be  120  kilograms.  (LABORATORY 
MANUAL,  Exercise  IV.) 

50.  Measurement  of  Capacity. — 
A  box  measuring  10  cm.  (or  1  dm.) 
on  each  inside  edge  has  a  volume  of 
1,000  cu.  cm.  (or  1  cu.  dm.).  The 
amount  of  liquid  it  will  hold  has 
been  named  the  liter  (pronounced 
leeter),  which  is  about  one  quart. 
Liquids  and  gases  in  large  quantities 

cm.    i.  How  many  grams    are  measured  by  the  liter.    Fractions 
would  i  cu.  dm.  of  water    of  the  liter  are  usually  expressed  as 
cubic  centimeters  or  as  the  decimal  of 
a  liter;  as,  275  cu.  cm.  or  .275  of  a  liter. 


1  g.  1  cu.  cm. 

FIG.   17.  —  MEASURES 
OF  WEIGHT 

A  small  box  1  cm.  on 
edge  would  have  a  volume 
of  1  cu.  cm.  and  would 
hold  1  g.  of  water.  A 
1-gram  weight  made  of 
brass  or  iron  would  not 
be  so  large  as  1  cu. 


weigh?  2.  What  prefix 
could  be  used  instead  of 
the  number  of  grams? 
3.  One  pound  is  equal 
to  the  weight  of  about 
450  g.  How  many 
pounds  in  1  kg.? 


1,000    cu.    cm.    is    always    1    liter,    but 
1,000  cu.  cm.  of  a  liquid  does  not  always 
weigh  1  kilogram. 
1,000  cu.  cm.  of  water  is  1  liter  of  water  and  weighs  1  kilogram. 
1,000  cu.  cm.  of  sea  water  is  1  liter  of  sea  water  and  weighs  about 
1.025  kilograms. 

1,000  cu.  cm.  of  sulphuric  acid  is  1  liter  of  sulphuric  acid  and  weighs 
1.8  kilograms. 


51.  Inertia.  —  A  book  resting  on  a  table  will  never  change 
its  own  position;  a  ball  thrown  on  smooth  ice  will  go  a  long 
distance  in  a  straight  line  before  it  stops.  This  inability  of 
a  body  to  change  its  own  state  of  motion  or  rest  is  called 
inertia.  If  a  body  is  at  rest,  it  tends  to  remain  at  rest;  if 
it  is  in  motion,  it  tends  to  continue  in  motion  in  a  straight 
line  with  unchanging  speed. 

Illustrations  of  this  law  of  inertia  are  seen  in  moving  cars. 


MATTER  AND  ITS  PROPERTIES  53 

People  are  standing,  and  while  the  car  moves  in  a  straight 
line  with  nearly  uniform  or  gradually  changing  velocity,  all 
is  well.  But  if  the  car  suddenly  stops,  people  are  thrown 
forward.  Their  feet  stop  when  the  car  does,  because  the 
weight  of  the  body  presses  the  feet  firmly  to  the  floor.  From 


FIG.  18.  —  MEASURES  OF  CAPACITY 

k 

Measures  of  liquids  and  small  solids  are  usually  in  the  form  of  a  cylinder. 
A  cylinder  which  holds  as  much  liquid  as  a  cu.  dm.  box  is  called  a  liter  (1.). 
It  holds  about  1  qt.  1.  To  how  many  cu.  cm.  is  1  1.  equivalent? 
2.  250  cu.  cm.  is  what  part  of  1 1? 

inertia,  the  upper  part  of  the  body  continues  in  motion  for- 
ward, as  the  result  shows. 

The  effect  of  the  sudden  starting  of  a  car  in  which  people 
are  standing  shows  the  inertia  of  bodies  at  rest;  that  is, 
their  tendency  to  remain  at  rest. 

52.  Special  Properties.  —  Extension,  weight,  and  inertia 
are  the  only  properties  which  belong  to  all  matter.  Different 
kinds  of  matter  have  different  special  properties.  Some  of 
the  special  properties  are: 

Hardness,  ability  to  resist  being  scratched.  A  diamond 
cannot  be  scratched  by  steel. 


54        FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 

Tenacity,  ability  to  resist  being  pulled  apart.  A  steel 
cable  bears  a  great  strain  without  breaking. 

Brittleness,  capability  of  breaking  under  a  sudden  blow  or 
shock.  Glass  is  a  substance  having  brittleness. 

Elasticity,  capability  of  regaining  its  shape  and  volume 
after  the  force  which  changes  the  form  is  removed.  A 
rubber  ball  which  has  been  flattened  becomes  round  again. 

Flexibility,  capability  of  bending  without  breaking.  A 
rope  is  flexible. 

The  terms  elasticity  and  flexibility  are  sometimes  confused. 
Rubber  is  flexible  —  it  will  bend;  it  is  also  elastic,  for  it 
unbends  when  the  bending  force  is  removed.  A  piece  of 
lead  is  flexible  —  it  will  bend;  but  it  is  not  very  elastic,  for 
it  remains  bent  when  the  bending  force  is  removed. 

These  properties,  and  many  others,  are  physical  proper- 
ties. 

53.  Properties  of  Living  Matter.  —  There  are  four  special 
properties  which  belong  to  all  living  matter  and  do   not 
belong  to  any  forms  of  non-living  matter.     The  properties 
or  characteristics  of  living  matter  are  called  physiological 
properties.     There  are  four  physiological  properties: 

Irritability,  the  property  of  responding  to  influences  from 
without.  The  tips  of  plant  roots  grow  toward  water. 

Spontaneous  motion,  power  to  change  the  position  of  the 
body  or  a  part  of  the  body.  Stems  twine  around  a  support; 
a  snake  glides  along  the  ground. 

Nutrition,  the  property  of  taking  up  certain  substances  to 
be  used  in  constructing  the  body.  Proper  food  and  air  are 
all  that  is  necessary  to  make  a  chicken  grow  to  be  a  fowl  of 
twenty  times  its  original  weight. 

Reproduction,  the  power  to  form  other  bodies  like  them- 
selves. Plants  form  seeds  and  animals  form  eggs,  from 
which  grow  new  bodies  like  themselves. 

54.  Organisms.  —  Bodies  having  physiological  properties 
are  called  organisms,  and  much  of  the  matter  of  which  they 


MATTER  AND  ITS  PROPERTIES  55 

are  composed  is  called  organic  matter.  The  blood  of  'an 
animal  and  the  sap  of  a  tree  are  organic  matter.  Grains  of 
sand  and  drops  of  pure  water  are  inorganic  matter;  they  have 
none  of  the  physiological  properties. 

EXERCISES 

1.  Name  some  bodies  composed  wholly  or  in  part  of  silver;  paper; 
stone;  iron;  rubber. 

2.  Name  the  principal  substance  in  a  book;    a  stove;    a  desk;    a 
tumbler;  a  shoe. 

3.  By  what  words  would  you  describe  a  piece  of  chalk? 

4.  What  are  the  characteristics  of  salt? 

5.  Name  the  properties  of  lead.     Tell  why  Ex.  3  and  Ex.  4  are 
of  the  same  kind  as  Ex.  5. 

6.  How  many  centimeters  are  there  in  3  m.  4  dm.  5  cm.? 

7.  Write   1,246  cm.  in  terms  of  several  different  units. 

8.  (a)  A  tank  is  1  m.  deep,  1.5  m.  long,  .75  m.  wide.     Find  its 
contents  in  cubic  meters. 

(6)  Write  the  dimensions  in  decimeters  and  find  its  contents  in 
cubic  decimeters. 

(c)  What  weight  of  water  would  fill  the  tank? 

9.  Why  do  people  who  are  standing  in  a  moving  car  tend  to  fall 
forward  if  the  car  stops  suddenly? 

10.  What  is  the  only  safe  way  to  alight  from  a  moving  vehicle? 
Give  reasons. 

11.  Describe  the  effect  on  upright  bodies  in  a  wagon,  when  it  sud- 
denly turns  a  right  angle. 

12.  Arrange  under  the  two  headings  —  organic  matter  and  inorganic 
matter  —  the  following  substances :   an   apple,  a  pebble,  silk,  cotton, 
chalk,  paper,  salt,  sugar,  wood,  brick,  bread,  granite,  silver,  milk,  ice. 


. 

CHAPTER  IV 
FORCE  AND   MOTION;    PHYSICAL  STATES  OF  MATTER 

55.  Force.  —  A  moving  object  attracts  attention,  and  it 
is  natural  to  ask,  "What  started  it?"     A  single  word  is 
the  answer:   force.     To  the  question,  "What  stops  it?"  the 
answer  is  the  same:    force.     Force  is  that  which  produces 
or  tends  to  produce  motion,  or  change  of  motion.      Force 
does  not  always  produce  motion.     A  man  uses  force  when 
he  pushes  against  a  wall,  but  the  wall  may  not  move.    A 
force  is  sometimes  described  as  a  push  or  a  pull. 

56.  Gravity.  —  The  force  which  causes  an  unsupported 
body  to  fall  toward  the  earth  is  called  gravity.     The  fall  is 
explained  by  saying  that  the  earth  attracts  or  pulls  the  body 
toward  itself.     It  is  gravity  which  causes  the  air  to  remain 
near  the  earth  and  to  move  with  it,  instead  of  being  left 
behind  as  the  earth  moves  around  the  sun  with  the  velocity 
of  a  cannon  ball. 

If  a  body  does  not  fall  toward  the  earth,  it  is  because  it 
is  kept  from  moving  by  some  opposing  force.  If  the  body 
is  held  in  the  hand,  gravity  is  opposed  by  muscular  force. 
If  it  rests  on  a  table,  gravity  is  opposed  by  cohesion,  which 
holds  the  fibers  of  wood  together.  If  it  is  suspended  by  a 
chain,  gravity  is  opposed  by  the  tenacity  of  iron. 

57.  Action   of   Two   Forces.  —  The  force  of  gravity  acts 
vertically  downward.     Any  force  which  opposes  it  must  act 
vertically  upward.     If  the  opposing  force  is  equal  to  gravity, 
the  body  remains  at  rest;  if  it  is  less  than  gravity,  the  body 
moves  downward;  if  greater,  the  body  moves  upward. 

The  effect  of  two  or  more  forces  acting  at  the  same  point 
is  called  the  resultant.  For  example,  a  body  weighing  30 

56 


FORCE  AND  MOTION  57 

pounds  is  pulled  upward  by  a  force  of  50  pounds.  The 
effect  will  be  motion  upward  as  if  a  force  of  20  pounds  were 
acting  alone.  Forces  and  their  resultants  are  described  in 
terms  of  weight  and  may  be  represented  by  lines.  A  force 
of  10  pounds,  for  instance,  may  be  represented  by  a  line  1 
inch  long.  In  the  same  case,  a  force  of  20  pounds  would 
be  represented  by  a  line  2  inches  long. 

Forces  also  act  horizontally  and  then  produce  motion  in 
a  horizontal  direction.  Two  forces  acting  in  the  same  direc- 
tion produce  an  effect  equal  to  the  sum  of  the  two  forces. 
Acting  in  opposite  directions,  they  produce  an  effect  equal 
to  the  difference  of  the  two  forces,  the  resultant  being  in  the 
direction  of  the  greater  force.  For  example,  two  horses 
working  together  can  move  as  great  a  load  as  the  two  horses 
working  singly.  When  a  man  rows  a  boat  up  stream,  his 
muscular  force  acts  in  a  direction  opposite  to  the  force  of  the 
current;  he  must  therefore  exert  a  force  greater  than  that 
of  the  current. 

If  forces  act  obliquely  or  at  right  angles  to  each  other, 
the  resultant  will  lie  between  them.  Suppose  the  current  of 
a  stream  is  directly  east;  a  man  in  a  motor  boat  sets  out 
exactly  south  with  the  rudder  set.  He  will  arrive  at  a  place 
down  stream  instead  of  opposite  the  point  where  he  started. 
The  direction  of  the  resultant  can  be  determined  by  a  simple 
mathematical  construction. 

Let  two  lines  at  right  angles  represent  two  forces  acting 
at  the  point  A .  If  the  horizontal  line  represents  a  force  of 
50  pounds  acting  east,  and  the  vertical  line  a  force  of  25 
pounds  acting  south,  the  resultant  will  be  represented  by 
the  diagonal  of  a  rectangular  figure  constructed  on  these 
lines.  Its  value  can  be  found  by  measurement,  letting  each 
inch  of  the  diagonal  represent  the  same  number  of  pounds 
as  an  inch  in  the  other  lines.  (See  Fig.  19,  p.  58.) 

58.  Friction.  —  A  ball  is  set  rolling  on  a  smooth  floor; 
a  boy  runs  upon. a  sheet  of  ice  and  then  slides.  Because  of 


58        FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 


inertia,  the  ball  and  the  boy  have  a  tendency  to  continue 
their  motion  in  the  same  direction  with  the  same  velocity 
as  at  first.  But  they  do  not  do  so.  They  gradually  roll  or 
slide  more  slowly,  until  each  finally  comes  to  rest.  Gravity 
caused  them  to  press  upon  the  surface  below,  and  this  rub- 
bing of  two  surfaces,  or  friction,  is  a  hindrance  to  motion. 
If  two  moving  parts  of  a  machine  rub  together,  it  takes  more 
power  to  make  them  move.  Oil  or  some  other  lubricant 
between  the  parts  reduces  the  friction,  because  oil  makes 
smoother  surfaces.  Friction  may  cause  reduced  speed  or 

loss  of  motion,  that  is,  rest. 
It  is  like  an  opposing  force 
in  its  effect. 

59.  Work.  —  If,  in  spite 
of  friction,  a  stone  is  moved 
along  the  ground,  work  is 
done.  Overcoming  resist- 
ance to  force  is  work. 
Muscular .  work  is  done  in 
lifting  a  body  in  spite  of 
the  resistance  offered  by  the 


4cm. 


FIG.  19.  —  Two  FORCES  ACTING  AT 
RIGHT  ANGLES 

AC  may  represent  a  force  of  100  kg. 


(1  cm.  =  25  kg.)  acting  toward  the  east     downward    pull  of   gravity. 

upon  the  point  A^    i.  what  force  and    Thework  of  the  steam  in  an 

what    direction    does     AB    represent' 

2.  If  the  force  AC  acted  alone,  to  what  engine  is  to  push  the  piston 
point  would  a  body  at  A  move?  If  rod  which  U  Qr  h 

AB  acted    alone?     3.  With   the   forces  *  ^ 

acting  together,  the  body  moves  to  D.    other  parts  of  the  machine. 

In  what  direction  does  it  move,  and  as  60<  Energy.— The  ability 
if  acted  upon  by  what  force?  &J  J 

to  do  work  is  called  energy. 

It  is  possessed  by  a  moving  body  or  by  a  body  in  such  a 
position  that  it  may  be  made  to  move.  A  baseball  which 
has  been  struck  has  energy;  it  may  overcome  the  resistance 
offered  by  a  pane  of  window  glass.  In  breaking  the  glass, 
the  ball  is  doing  work,  and  that  requires  energy  as  well  as 
putting  a  new  pane  in  place.  Suppose  that  an  iron  beam 
is  being  lifted  to. its  place  in  the  framework  of  a  building. 


FORCE  AND  MOTION  59 

The  cable  attached  to  the  beam  slips  off  and  the  beam  falls 
downward,  crashing  through  obstacles  and  doing  great  de- 
structive work.  While  suspended  and  motionless,  the  beam 
had  energy;  it  was  capable  of  falling  and  doing  work.  The 
ordinary  use  of  the  word  work  implies  necessary  or  useful  mo- 
tion, but  in  scientific  use  the  act  of  overcoming  any  resistance 
is  work. 

61.  Machines.  —  A  machine  is  any  instrument  by  means 
of  which  work  is  advantageously  done.  It  may  be  very 
simple;  as  the  lever,  a  stiff  bar  by  which  a  man  can  move  a 
much  heavier  weight  th^n  he  could  move  without  a  machine. 
Another  simple  machine  is  the  pulley,  which  consists  of  a 
wheel  over  which  a  rope,  chain,  or  belt  is  moved,  so  as  to 
lift  a  weight  at  one  end  when  a  force  pulls  on  the  other  end. 
The  wheel  and  axle  consists  of  a  cylinder  and  a  wheel  fastened 
together  and  moving  upon  the  same  axis.  The  cylinder, 
which  is  the  "axle,"  winds  up  a  rope  or  cable  that  pulls  or 
lifts  heavy  weights.  The  wheel  is  often  furnished  with  a  crank 
or  spokes  by  which  the  whole  machine  is  turned.  Houses 
are  moved  by  this  machine,  operated  by  horses. 

Another  simple  machine  is  the  screw,  which  is  generally 
made  of  metal  or  wood.  It  is  a  cylinder  having  a  ridge, 
called  the  thread,  winding  spirally  around  it.  The  screw 
works  in  a  nut  that  has  a  groove  to  fit  the  thread  of  the 
screw.  The  screw  is  turned  by  hand  or  other  power,  and  is 
used  in  small  presses  and  in  machines  for  raising  weights. 
It  is  sometimes  used  to  raise  buildings.  Several  parts  of 
the  underpinning  of  a  building  are  removed  and  a  screw  is 
put  in  each  of  these  places.  Every  turn  of  the  screw  lifts 
the  part  above  it  by  the  width  between  the  threads.  The 
original  screw  propeller  (1850)  of  a  steamship  really  screwed 
its  way  through  the  water,  pushing  the  water  to  one  side 
as  a  small  screw  pushes  wood.  Later  modifications  have 
produced  a  propeller  which  does  not  resemble  a  screw  in 
form. 


60       FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 


FIG.  20. —  THE  LEVER 


FIG.  21.  — PULLEYS 


FIG.  22.  —  WHEEL  AND  AXLE 

FIGS.  20-23.  —  SIMPLE  MACHINES 

Two  advantages  are  derived  from  the  use  of 
simple  machines:  the  power  can  be  applied  in  various 
directions;  and  by  the  right  adjustment,  a  small 
power  can  move  a  weight  greater  than  itself.  For 
example,  to  take  a  stone  from  its  place  requires 
lifting  (that  is,  pulling  upwards)  by  a  force  equal 
at  least  to  the  weight.  By  means  of  a  stiff  bar 
resting  on  a  support,  called  the  fulcrum,  between 
the  stone  and  the  workman,  he  can  move  the  stone 
by  pushing  down  instead  of  lifting. 

1.  Why  is  it  easier  to  push  down  than  to  pull 
FIG.  23. — THE  SCREW   up?     2.  If  the  fulcrum  is  1  ft.  from  the  stone  and 
P  is    applied    3    ft.    from    the    fulcrum,  the   stone 

can  be  moved  by  applying  only  \  as  many  pounds  of  power  as  the  weight 
of  the  stone.  The  distances  of  P  and  W  from  the  fulcrum  are  as  3  to  1, 
which  makes  it  possible  for  a  given  power  to  lift  a  weight  three  times  as 
great  as  the  power  itself.  If  the  stone  weighs  450  lb.,  what  power  would 
be  needed  to  move  it? 


FORCE  AND  MOTION  61 

The  advantage  in  using  the  pulley  at  the  left  (Fig.  21)  is  simply  change 
of  direction.  A  50-lb.  weight  is  balanced  by  P,  which  =  50  Ib.  +  enough  to 
overcome  resistance  in  the  machine.  There  are  two  advantages  in  the 
use  of  the  pulley  at  the  right.  W  is  supported  by  2  cords,  each  of  which 
bears  half  the  weight  of  W  +  the  weight  of  the  pulley  block.  P  must 
balance  the  weight  supported  by  one  cord.  3.  Disregarding  internal 
resistance,  what  P  will  balance  550  Ib.  in  the  first  pulley?  4.  What  P  in 
the  second? 

5.  Where  is  P  applied  to  the  wheel  and  axle  (Fig.  22)?  In  what  direc- 
tion and  how  far  does  P  move?  6.  In  what  direction  does  W  move?  How 
far  does  it  move  for  one  turn  of  the  axle? 

The  thread  of  a  screw  fits  a  groove  in  the  nut,  which  hi  Fig.  23  is  the 
base  of  the  screw.  At  the  beginning  of  operation,  the  head  of  the  screw 
rests  upon  the  nut;  spokes  are  thrust  into  the  head  of  the  screw  by  which 
to  turn  it.  If  used  in  lifting  great  weights,  as  in  house  moving,  several 
men  can  be  employed.  As- the  head  makes  one  turn,  the  screw  and  the 
weight  upon  it  rise  as  much  as  the  distance  between  the  threads.  7.  The 
threads  of  a  set  of  jack  screws  are  2  in.  apart;  how  many  turns  are  needed 
to  raise  a  building  1  ft.? 

Complex  machines,  such  as  bicycles,  sewing  machines,  egg 
beaters,  or  gas  engines,  are  combinations  and  modifications 
of  these  simple  machines  and  a  few  others.  (See  Fig.  24, 
p.  62.) 

The  force  used  in  a  machine  is  called  the  power  (P), 
whether  it  is  the  muscular  force  of  man  or  animal,  the  pull 
of  gravity,  or  the  push  of  steam.  The  resistance  to  be  over- 
come is  called  the  weight  (W).  It  may  be  a  block  of  stone 
to  be  lifted,  a  bale  of  hay  to  be  compressed,  or  a  building  to 
be  moved.  Any  resistance  which  the  machine  itself  furnishes, 
on  account  of  stiffness  of  ropes  and  friction  between  parts 
of  the  machine,  is  included  in  W. 

62.  Experiments.  —  An  experiment  is  an  attempt  to  find 
out  the  truth  from  observation  of  things  themselves  rather 
than  from  what  others  have  learned  and  written  about  them. 

When  a  piece  of  wood  is  placed  on  one  pan  of  a  balance, 
that  side  goes  down.  We  place  a  piece  of  stone  there  with 
the  same  result.  We  exchange  that  for  paper  or  feathers, 
and  always  that  side  of  the  balance  goes  down.  We  ask 
ourselves,  "Why?" 

If  we  conclude,  after  many  experiments,  that  it  is  because 
there  is  more  matter  to  be  attracted  toward  the  earth  on 


62        FIRST  YEAR  COURSE   IN   GENERAL  SCIENCE 


one  side  of  the  balance  than  on  the  other,  we  have  answered 
the  question.  By  repeating  the  same  experiment  in  many 
ways  and  under  various  conditions,  we  may  arrive  at  certain 

conclusions  which  can 
be  summed  up  as  a 
definite  law. 

In  an  elementary 
course  in  science,  we 
cannot  expect  to  dis- 
cover any  new  laws  or 
even  to  prove  any  of 
the  old  laws.  All  that 
we  can  do  is  to  satisfy 
ourselves  that  these 
great  laws  which  others 
have  discovered  hold 
true  as  far  as  we  have 
the  means  to  observe 
them. 

The  place  where  ex- 
periments are  made  is 
called  a  laboratory. 
The  word  means  "  work- 
shop." 

63.  Apparatus. — The 
things  with  which  we 
work,  such  as  balances, 
rulers,  thermometers, 
microscopes,  gas 
burners,  and  glass 
tubes,  are  called  pieces 


FIG.  24.  —  A  COMBINATION  OF  SIMPLE 
MACHINES 

This  rotary  crane  is  such  as  is  used  in 
unloading  ships,  and  in  constructing  dams, 
bridges,  and  great  buildings.  It  shows  a 
combination  of  a  lever,  pulleys,  and  wheel 
and  axle.  The  lever,  called  the  jib,  is 
fastened  at  one  end  to  an  upright  post,  with 
which  it  rotates,  so  that  the  load  it  supports 
can,  after  being  lifted,  be  deposited  else- 
where. The  cable,  which  supports  and  lifts, 
runs  over  pulleys  and  is  wound  up  on  the 
drum  of  a  wheel  and  axle.  How  much  will 
the  load  rise  if  the  cable  is  wound  once 


around  a  drum  2  ft.  in  diameter? 

of    apparatus.      They 

should  be  handled  with  care,  kept  in  good  order,  and  re- 
turned to  their  proper  places. 

The  weight  of  a  body  is  determined  by  the  use  of  a  piece 


FORCE  AND  MOTION 


63 


of  apparatus  or  machine  called  a  balance,  and  the  process  of 
finding  the  weight  is  really  an  experiment  with  gravity  as  a 
force. 

64.  Weighing.  —  There   are  two  common  forms  of  ma- 
chines for  weighing:   the  spring  balance  and  the  equal-arm 
balance.     In  the  spring  balance,  the  body  to  be  weighed  is 
hung  on  a  hook  attached  to  a  spiral  spring.     This  causes  the 
spring  to  extend,  more  or  less,  according 

to  its  stiffness  and  the  weight  of  the 
body.  By  means  of  a  scale  near  the 
spring,  we  can  learn  the  pull  which 
the  earth  exerts.  We  call  this  weigh- 
ing; it  is  measuring  the  force  with 
which  gravity  acts  upon  the  body. 
Therefore  weight  is  the  measure  of  the 
earth's  attraction  for  a  body. 

Another  method  of  weighing  is  by 
the  use  of  some  form  of  an  equal-arm 
balance.  A  horizontal  bar  is  supported 
at  the  middle  in  such  a  way  that  it  is 
free  to  swing  up  or  down  at  either  end. 
The  bar  will  be  horizontal  if  bodies 
of  equal  weight  are  placed  on  the  pan 
or  platform  attached  to  each  end.  To 
weigh  a  body,  we  place  it  on  one  pan 
or  platform,  and  on  the  other  we  place 
certain  bodies  of  known  weight  that 
bring  the  bar  to  a  horizontal  position. 
(LABORATORY  MANUAL,  Exercise  V.) 

65.  Density.  — One  of  the  important 
properties  of  a  substance  is  its  density. 
The  term  density  has  an  exact  mean- 
ing.    We  say  that  the  weight  of  a  body  is  the  amount  of 
matter  which,  however  large  or  small,  it  contains.     Density 
is  the  amount  of  matter  in  a  unit  of  volume.     For  example, 


FIG.  25.— THE  SPRING 
BALANCE 

1.  JVhen  a  body  is 
suspended  from  the 
hook,  the  spiral  wire  to 
which  it  is  attached  is 
partially  straightened. 
What  straightens  it? 

2.  When    the    body    is 
removed,  what  property 
of   the   wire   is   shown? 

3.  Would  steel  or   lead 
be  the  better  wire  for  a 
balance?     Why? 


64        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

a  block  of  stone  weighs  1,500  kilograms;  a  piece  of  iron, 
much  smaller,  weighs  15  kilograms.  The  piece  of  iron  is 
much  lighter  than  the  block  of  stone.  But,  on  the  other 
hand,  1  cubic  centimeter  of  the  stone  weighs  3.5  grams; 
1  cubic  centimeter  of  iron  weighs  7.8  grams.  The  iron  has 
more  matter  in  a  cubic  centimeter,  or  a  cubic  inch,  or  a 
cubic  foot,  than  the  stone  has.  The  density  of  the  iron  is 
greater. 

In  the  British  system,  in  which  the  cubic  foot  is  the  unit 
of  volume  and  the  pound  the  unit-  of  weight,  the  density  of 


FIG.  26.  —  PLATFORM  SCALES 

This  form  of  balance  is  an  application  of  the  lever.  The  pans  or 
platforms  are  at  the  end  of  a  bar  which  is  supported  at  the  middle.  1.  With 
nothing  on  either  platform,  the  bar  is  horizontal.  Why?  2.  Under  what 
other  conditions  will  the  bar  be  horizontal?  3.  What  is  its  position  with 
100  g.  on  one  platform  and  90  g.  on  the  other?  Why? 

a  substance  is  the  weight  in  pounds  of  one  cubic  foot  of  that 
substance.  One  cubic  foot  of  water  weighs  62.5  pounds; 
therefore  the  density  of  water  is  62.5  pounds  per  cubic  foot. 
One  cubic  foot  of  marble  weighs  168.5  pounds;  therefore  the 
density  of  marble  is  168.5  pounds  per  cubic  foot. 

In  the  metric  system,  in  which  the  cubic  centimeter  is  the 
unit  of  volume  and  the  gram  the  unit  of  weight,  the  density 
of  a  substance  is  the  weight  in  grams  of  one  cubic  centimeter 


FORCE  AND   MOTION 


65 


800 


of  that  substance.  One  cubic  centimeter  of  water  weighs 
one  gram;  therefore  the  density  of  water  is  one  gram  per 
cubic  centimeter. 

66.   Methods    of    Finding   the    Density  of   a    Solid.  - 
It  is  not  a  difficult  matter  to  find 
the   density   of    a    substance    by 
experiment. 

When  the  substance  is  in  the 
form  of  a  regular  solid,  such  as 
a  sphere,  cylinder,  or  cube,  the 
volume  can  be  calculated  from 
measurement  of  the  dimensions. 
Determine  the  volume  by  measure- 
ment of  dimensions,  and  the  weight 
by  use  of  balances.  Then  divide 
the  number  representing  the  weight 
in  grams  by  the  number  repre- 
senting the  volume  in  cubic  centi- 
meters. If  a  block  of  iron  con- 
taining 30  cubic  centimeters  weighs 
234  grams,  1  cubic  centimeter 
weighs  7.8  grams.  Its  density, 
then,  is  7.8  grams  per  cubic  centi- 
meter. 

When     the     snbstanpp     had     an  A,  measurin8   Slass   con- 

nas    an    tainej  640  cu  cm  of  water 

irregular  form,  its  density  can  be    A  piece  of   stone  was  sus- 


400 


FIG.  27.  —  FINDING  THE 
VOLUME  .OF  A  SOLID 
BY  DISPLACEMENT  OF 
WATER 


1.  What  was  the  volume  of 
the  stone?  2.  How  do  you 
know? 


found   in  the  following  way,  pro- 

vided  the  substance  will  sink  and 

will   not   dissolve  in  water.     First 

find    its    weight.      Then    take    a 

measuring  glass,  which  has  lines  on  the  side  to  show  the 

amount  of  liquid  which  it  contains.      Pour  water  into  the 

glass,  perhaps  to  the  200  cu.  cm.  line.      Tie  a  thread  about 

the  body  and  let  it  down  into  the  water.      The  water  rises 

in  the  glass,  because  two  bodies  cannot  occupy  the  same 


66        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

space  at  the  same  time.  If  the  water  reaches  the  230  cu. 
cm.  line,  the  solid  must  have  displaced  30  cubic  centimeters 
of  water.  Therefore  its  volume  is  30  cubic  centimeters.  If 
the  weight  is  96  grams,  its  density  is"  3.2  grams  per  cubic 
centimeter.  (LABORATORY  MANUAL,  Exercise  VI.) 

67.  Finding  the  Density  of  a  Liquid.  —  The  density  of 
a  substance  in  the  liquid  form  may  be  found  in  the  following 
way.     Find  the  capacity  of  a  flask  or  bottle  by  weighing  it, 
first  empty,  and  then  filled  with  water.     If  the  flask  when 
filled  with  water  weighs  75  grams  more  than  when  empty, 
the  capacity  of  the  bottle  is  75  cubic  centimeters,  because 
1  cubic  centimeter  of  water  weighs  1  gram.     Then  find  the 
weight  of  the  given  liquid  that  is  required  to  fill  the  same 
bottle;  for  example,  79  grams.     Make  the  same  calculation 
as  in  finding  the  density  of  a  solid ;  that  is,  divide  the  weight 
of  the  liquid  by  the  volume.     79  g.  -=-  75  (cu.  cm.)  =  1.05  g. 
per    cu.    cm.,   density.     (LABORATORY   MANUAL,    Exercises 
VII  and  VIII.) 

68.  Specific   Gravity.  —  The   expression   specific  gravity 
is   used  to  denote  the  relation   between  the  weight  of   a 
body  and   the  weight  of  an  equal  volume  of  water.     It  is 
really  a  comparison  of  densities.     Specific  gravity  can  be 
determined  by  experiment  without  knowing  the  volume  of 
a  body. 

It  is  well  known  that  bodies  seem  to  weigh  less  in  water 
than  in  air.  It  has  been  proved  by  repeated  experiments 
that  this  apparent  loss  of  weight  is  always  the  same  as  the 
weight  of  the  water  displaced.  The  volume  of  water  dis- 
placed is,  of  course,  equal  to  the  volume  of  the  body 
immersed.  Therefore  the  apparent  loss  of  weight  is  the 
"  weight  of  an  equal  volume  of  water."  Hence,  if  we  divide 
the  weight  of  the  body  in  air  by  its  apparent  loss  of  weight 
in  water,  we  get  the  specific  gravity. 

For  example,  a  piece  of  marble  weighs  230  grams.  When 
suspended  from  a  balance  so  that  it  hangs  in  water,  its 


FORCE  AND  MOTION  67 

weight  is  145  grams.  The  apparent  loss  of  weight  is  85 
grams.  230  g.  -=-  85  g.  =  2.7  (specific  gravity).  Therefore, 
the  weight  in  air  is  2.7  times  the  weight  of  the  water  dis- 
placed, or  2.7  times  the  weight  of  a  volume  of  water  equal 
to  that  of  the  marble.  (LABORATORY  MANUAL,  Exercise 
IX.) 

69.  Physical  States  of  Matter.  —  There  are  three  states 
or  conditions  of  matter:    solid,  liquid,  and  gaseous.     Most 
substances  have  been  obtained  in  all  three  states. 

Matter  is  said  to  be  solid,  or  in  the  solid  state,  when  it 
opposes  any  change  in  its  shape.  Much  energy  is  required  to 
separate  the  molecules  of  a  solid.  Wood,  iron,  nails,  and 
sand  are  solids. 

Matter  is  said  to  be  liquid,  or  in  the  liquid  state,  when  it 
has  no  definite  shape  of  its  own,  but  will  take  the  shape  of 
any  vessel  into  which  it  is  poured.  It  will  oppose  strongly, 
however,  any  change  in  its  volume.  Water,  milk,  kerosene, 
and  mercury  are  liquids. 

Matter  is  said  to  be  a  gas,  or  in  the  gaseous  state,  when 
it  has  no  definite  shape  or  volume  of  its  own;  if  put  into 
a  vessel,  it  will  distribute  itself  throughout  all  the  space  in 
the  vessel,  whatever  the  size  or  form.  Air,  hydrogen,  illumi- 
nating gas,  and  steam  are  gases. 

70.  The   Effect    of    Heat   on    Physical    State.  —  Many 
solids,  on  being  heated,  are  changed  into  liquids.     Examples: 
ice,  lead,  lard.     When  these  liquids  are  cooled,  they  change 
back  to  the  solid  state.     Many  liquids,  on  being  heated, 
change  into  gaseous  substances  called  vapors.     Vapors  are 
gases  which  condense  at  ordinary  temperatures.     Steam,  the 
gas  made  by  boiling  water,  is  a  vapor.     The  gas  from  boil- 
ing alcohol  is  a  vapor.     The  gases  of  which  the  air  is  com- 
posed are  not  vapors. 

The  temperature  at  which  a  solid  begins  to  be  liquid  is 
called  the  melting  point  of  the  substance.  Every  substance 
that  can  be  melted  has  its  own  melting  point.  Iron  melts 


68        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

at  a  much  higher  temperature  than  lead,  but  at  a  much 
lower  temperature  than  platinum. 

If  a  liquid  is  sufficiently  cooled,  it  returns  to  the  solid 
state.  The  highest  temperature  at  which  it  does  this  is 
called  the  temperature  of  solidification  or  the  freezing  point. 
The  freezing  point  of  water  is  32°  F.;  of  sea  water,  28°  F.; 
of  sulphur,  240°  F.;  of  copper,  2000°  F. 

The  temperature  of  solidification  and  the  melting  point 
are  the  same  for  a  given  substance.  If  a  thermometer  is 
placed  in  cracked  ice  in  a  room  of  moderate  temperature, 
it  will  show  the  temperature  of  the  melting  mass  to  be 
32°  F.  If  the  thermometer  were  placed  in  water  out  of 
doors  on  a  cold  winter  day,  the  temperature  of  the  freezing 
water  would  be  32°  F. 

The  temperature  at  which  a  substance  changes  from  the 
liquid  to  the  gaseous  form,  when  heated  in  an  open  vessel, 
is  called  its  boiling  point.  For  water,  this  temperature  is 
212°  F.  On  the  other  hand,  if  a  gas  is  cooled  sufficiently, 
it  will  condense  or  change  into  the  liquid  form.  The  high- 
est temperature  at  which  the  gas  condenses  is  the  same  as 
the  boiling  point  of  the  liquid  which  it  forms. 

71.  Distillation.  —  When  water  and  other  liquids  are 
changed  into  the  gaseous  form  by  boiling,  many  of  the  im- 
purities which  were  dissolved  in  the  liquid  do  not  change  to 
a  vapor.  Hence,  if  the  vapor  is  collected  in  a  separate 
vessel  and  cooled  until  it  condenses,  a  product  purer  than 
the  original  liquid  may  be  obtained.  This  process  is  called 
distillation,  and  the  product  formed  by  the  condensed  vapor 
is  called  the  distillate. 

When  a  mixture  of  two  or  more  liquids  is  heated,  the  in- 
gredients become  gases  at  different  temperatures,  because 
each  substance  has  its  own  boiling  point.  The  ingredient 
with  the  lowest  boiling  point  escapes  as  a  vapor  first.  If 
a  mixture  contains  three  liquids  whose  boiling  points  are 
150°,  180°,  and  212°  respectively,  the  liquids  can  be  sepa- 


FORCE  AND  MOTION"  60 

rated  by  fractional  distillation.  That  is,  if  the  mixture  is 
heated  to  a  temperature  of  150°,  the  substance  which  boils 
at  that  temperature  will  change  into  vapor  and  can  be 
cooled  and  condensed  in  a  tube  through  which  it  passes 
off.  Then  if  the  temperature  is  raised  to  180°,  the  liquid 
of  that  boiling  point  vaporizes.  This  is  called  fractional 
distillation. 

72.   Uses   of   Distillation.  —  It  is  sometimes  necessary  at 
sea  to  distill  sea  water  in  order  to  have  water  that  contains 


FIG.  28.  —  DISTILLATION 

The  glass  retort  might  contain  sea  water,  or  a  solution  of  blue  vitriol, 
or  molasses  and  water.  1.  On  being  heated  to  212°  F.,  the  same  vapor 
would  come  out  in  each  case.  What  vapor?  2.  Why  is  water  kept  run- 
ning over  the  neck  of  the  retort? 

no  salt,  for  use  in  the  boilers  and  for  drinking.  The  distillate 
is  fresh  water. 

Alcohol  is  distilled  from  liquids  prepared  from  fruits, 
grains,  potatoes,  and  other  plant  material. 

Kerosene,  benzine,  gasolene,  and  other  liquids  can  be 
separated  from  petroleum  and  from  one  another,  because 
they  have  different  boiling  points.  Gasolene  has  a  lower 
boiling  point  than  benzine;  and  benzine,  a  lower  one  than 
kerosene. 


70        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


EXERCISES 

1.  A  force  of  50  kg.  is  acting  toward  the  west,  and  one  of  75  kg. 
toward  the  east.     What  is  the  resultant  force  and  what  is  the  direc- 
tion of  motion? 

2.  If   the  force  of  50  kg.  in  Ex.  1   acted  toward  the  east,  what 
would  be  the  resultant  force  and  the  direction  of  motion? 

3.  Represent  a  force  of  100  Ib.  acting  east  by  a  line  2  in.  long,  and 
a  force  of  200  Ib.  acting  north  by  a  line  4  in.  long  at  right  angles  to  the 
first  line.     Draw  with  dotted  lines  two  sides  opposite  and  parallel  to 
these,  making  a  four-sided  figure.     Draw  the  diagonal  line  between  the 
two  force  lines.     That  represents  the  resultant  force.     Measure  it  and 
compute  its  value,  if  1  in.  represents   a  50-pound    force.     State  the 
magnitude  and  direction  of  the  resultant. 

4.  Represent  a  force  of  25  g.  acting  southeast  and  one  of  50  g.  acting 
north.     Draw  the  other  two  sides  of  the  figure  parallel  to  the  first  two. 
Measure  the  diagonal  between  the  force  lines  and  compute  its  value. 
Which  force  does  it  more  nearly  approach  in  direction?     Why? 

6.   A  block  of  stone  30  x  25  x  100  cm.  weighs  225  kg.    (1  kg.  equals 
1,000  g.)     Calculate  its  density. 

6.  A  block  of  wood  of   the  dimensions   given  in   Ex.   5  weighs 
54,625  g.     Calculate  its  density. 

7.  The  density  of  ice  is  .93  g.  per  cubic  centimeter.     What  is  its 
specific  gravity?     If  put  into  water,  will  it  sink  or  float?     Why? 

8.  A  rough  piece  of  granite  weighs  in  air  375  kg.     In  the  water  it 
weighs  250  kg.     What  is  its  specific  gravity?     What  is  its  volume? 
From  its  specific  gravity,  determine  the  density. 

9.  An  irregular  piece  of  brass  weighs  5  Ib.  9  oz.  in  air;   4  Ib.  14  oz. 
in  water.     Find  its  specific  gravity. 


CHAPTER  V 
HEAT:    ITS  DISTRIBUTION  AND   MEASUREMENT 

73.  Sources    of    Heat.  —  The  principal  sources  of  heat 
are: 

Chemical  action,  as  in  the  case  of  burning. 
Friction,  as  when  a  match  is  rubbed  on  a  rough  surface. 
Compression,  as  when  the  tube  of  a  bicycle  pump  becomes 
hot  because  the  air  in  it  has  been  repeatedly  compressed. 

74.  Effects  of  Heat.  —  In  the  study  of  the  physical  states 
of  matter,  it  was  shown  that  heat  changes  the  physical  con- 
dition from  solid  to  liquid,  and  from  liquid  to  gas;   but  the 
first  effect  of  heat  is  to  raise  the  temperature,  the  next  to 
increase  the  volume.     Heat  is  recognized  as  a  form  of  energy 
because  it  overcomes  the  force  which  holds  particles  of  mat- 
ter together,  and  separates  the  molecules,  causing  expansion. 

Many  compounds,  on  being  heated  to  a  high  temperature, 
separate  into  two  or  more  substances  (some  of  which  are 
gases),  without  first  melting.  This  is  the  case  with  wood, 
paper,  and  similar  compounds.  Charcoal  is  made  by  heat- 
ing wood  in  a  partly  covered  space,  without  burning  it. 
During  the  process  of  heating,  a  heavy  yellowish  smoke 
comes  from  the  wood,  and  a  sticky  dark  substance,  known  as 
wood  tar,  collects  on  the  inside  of  the  charcoal  kiln.  The 
solid  which  remains  is  charcoal.  (See  Fig.  29,  p.  72.) 

75.  The  Thermometer.  —  Change  of  temperature  is  some- 
times known  by  the  sense  of  feeling,  but  it  is  more  accurately 
shown  by  means  of  a  thermometer.     The  sense  of  feeling 
often  reports  comparative  temperature  only.     For  example, 
if  a  person  puts  one  hand  into  hot  water  and  the  other  into 
cold  water  for  a  time,  and  then  puts  both  hands  into  warm 

71 


72        FIRST  YEAR  COURSE   IN   GENERAL  SCIENCE 


water,  the  sensation  is  different  in  the  two  hands.  The 
water  feels  cold  to  the  hand  which  has  been  in  hot  water  and 
hot  to  the  one  which  has  been  in  cold  water.  This  shows 
that  the  body  sense  is  not  an  accurate  test  of  temperature. 
An  instrument  for  measuring  the  temperature  of  a  sub- 
stance is  a  thermometer.  It 
consists  of  a  glass  tube  with  a 
bulb  or  enlargement  at  one  end. 
To  make  a  thermometer,  the 
bulb  and  part  of  the  tube  are 
filled  with  mercury  (sometimes 
called  quicksilver),  and  then 
the  air  is  removed  from  the 
upper  part  of  the  tube  and  the 
tube  is  sealed.  The  sealed  tube 
and  bulb  are  placed  in  melting 
ice  and  the  point  at  which  the 
mercury  then  stands  is  marked 
freezing  point.  On  the  Fahren- 
heit thermometer,  commonly 
used  in  this  country,  the  freezing 
point  is  at  32°. 

If  heat  is  then  applied  to  the 
water  around  the  thermometer, 
the  mercury  begins  to  rise  in 
the  tube  as  soon  as  all  the  ice 
is  melted.  The  temperature 
does  not  change  until  the  ice 
is  melted,  because  the  heat 
energy  is  used  up  in  changing 
the  solid  to  a  liquid.  The  heat 
expands  the  mercury  in  the 
bulb  and  it  must  therefore  rise  in  the  tube.  It  continues 
to  rise  until  the  water  boils  and  then  the  mercury  remains 
stationary.  The  temperature  will  remain  constant  until 


FIG.  29.  —  HEATING  WOOD  IN 
A  TEST  TUBE 

Some  dry  pieces  of  wood 
are  put  into  a  test  tube  and 
heated  until  the  tube  is  red  hot. 
1.  What  kind  of  change  has  oc- 
curred in  the  tube  itself?  2.  The 
wood  does  not  melt;  it  does  not 
burn  because  heat  expanded  the 
air  so  that  nearly  all  of  it  left  the 
tube;  gas  and  smoke  come  from 
the  wood,  which  grows  black. 
What  kind  of  change  has  taken 
place  there?  3.  Why  do  you 
think  it  was  such? 


HEAT:    DISTRIBUTION  AND  MEASUREMENT 


73 


the  water  is  all  changed  to  steam,  for 
the  heat  energy  is  now  used  in 
changing  the  liquid  to  a  gas. 

The  temperature  which  indicates 
the  boiling  point  of  water  is  marked 
212°  on  the  Fahrenheit  thermometer. 
The  space  on  the  scale  between  32 
and  212  is  divided  into  180  equal 
parts,  each  one  of  which  is  a  degree. 

On  the  scale  of  the  Centigrade 
thermometer,  the  freezing  point  of 
water  is  marked  0°  and  the  boiling 
point  100°.  The  change  .of  tempera- 
ture between  0°  and  100°  C.  is,  of 
course,  the  same  as  between  32°  and 
212°  F.,  and  the  change  of  tempera- 
ture of  one  degree  C.  is  therefore 
greater  than  of  one  degree  F.  The 
Centigrade  thermometer  is  used  in 
most  laboratories  and  in  general  scien- 
tific work,  and  for  all  measurements 
of  temperature  in  many  countries. 


To  change  degrees  Centigrade  to  degrees 
Fahrenheit :  multiply  the  number  of  degrees 
by  1.8  (or  f)  and  add  32.  Example:  (100° 
C.X  1.8)  +32=  212°. 

To  change  degrees  Fahrenheit  to  degrees 

Centigrade:  from  the  number  of  degrees  sub-   FIG.  JO.  —  .LABORATORY 
tract  32  and  divide  the  remainder  by  1.8  or  f. 

fy-t  oo    T7i  QO° 

Example:   -  —  =  100°C. 


THERMOMETER 

1.  In  what  respects  is 


1.8 


a  laboratory  thermometer 
different  from  an  ordi- 
nary house  thermometer? 
2.  Why  are  these  differ- 


Since    mercury    becomes    solid    at 
about  40°  below  zero,  mercury  ther-  € 
mometers  are  not  used  for  very  low  temperatures.     Alcohol 
has  a  much  lower  freezing  point  than  mercury  and  for  this 


74        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

reason  alcohol  thermometers  are  used  in  cold  climates. 
Because  alcohol  is  cheaper  than  mercury,  colored  alcohol 
is  much  used  in  ordinary  thermometers.  (LABORATORY 
MANUAL,  Exercise  X.) 

76.  Conduction.  —  Whenever  the  temperature  of  a  body 
is  higher  than  that  of  its  surroundings,  it  gives  out  some  of 
its  heat.  There  are  three  methods  by  which  heat  is  dis- 
tributed: conduction,  convection,  and  radiation. 

If  two  bodies  of  different  temperatures  are  in  contact, 
after  a  time  the  temperature  of  the  colder  body  will  rise 


FIG.  31.  —  CONDUCTION  OF  HEAT 

Phosphorus  takes  fire  at  a  low  temperature.  1.  If  a  piece  of  phosphorus 
is  placed  on  a  strip  of  metal  and  the  metal  is  heated  at  a  distance  from  it, 
the  phosphorus  soon  burns.  Why?  2.  Why  in  Fig.  31  do  not  both 
pieces  ignite  at  once? 

and  that  of  the  warmer  will  fall.  If  one  end  of  a  cold 
iron  rod  is  heated  in  a  fire,  the  end  in  the  fire  will  soon 
become  red-hot  and  the  other  end  warm.  The  end 
farther  from  the  fire  is  heated  by  conduction.  Heat  has 
passed  from  molecule  to  molecule  until  the  one  farthest 
from  the  source  of  heat  has  received  it.  After  the  source  of 
heat  is  removed,  the  distribution  continues  until  all  parts 
of  the  bar  are  of  the  same  temperature.  The  iron  is  said  to 
be  a  conductor.  All  the  metals  are  heat  conductors. 


HEAT:    DISTRIBUTION  AND  MEASUREMENT         75 

If  the  hand  touches  an  object  having  a  temperature  lower 
than  the  hand  itself,  the  object  feels  cold  because  it  conducts 
heat /row  the  hand.  If  the  object  has  a  higher  temperature 
than  the  hand,  it  feels  warm  because  it  conducts  heat  to  the 
hand.  Bodies  which  have  been  for  a  long  time  in  the  same 
room  have  the  same  temperature,  but  the  good  conductors 
feel  cold,  the  poor  ones  less  cold. 

Metals  are  the  best  conductors  of  heat ;  stone,  hard  wood, 
silk,  and  linen  are  very  good  ones;  asbestos,  wool,  paper, 
and  air  are  poor  conductors.  Because  of  the  layers  of  air 
between  articles  of  our  clothing,  several  thin  garments  are 
warmer  than  one  thick  layer  of  the  same  weight  as  all  the 
thin  ones.  Clothing  does  not  make  us  warm  but  keeps  us 
warm  if  heat  is  not  conducted  away  from  the  body. 

77.  Convection.  —  Heat    is    distributed   through   liquids 
and  gases  by  moving  currents.     This  method  is  called  con- 
vection.    It  may  be  illustrated  by  studying  a  kettle  of  water 
over  a  fire.     The  bottom  of  the  kettle  becomes  heated,  and 
the  layer  of  water  in  contact  with  it  is  heated  by  conduction. 
This  rise  in  temperature  causes  expansion  in  the  bottom  layer 
and  therefore  a  smaller  density.     One  gram  of  cold  water 
occupies  one  cubic  centimeter  of  space;   when  the  water  is 
warmed,  a  gram  occupies  more  than  one  cubic  centimeter. 
One  cubic  centimeter  of  warm  water  weighs  less  than  one 
gram.     The  lighter,  warmer  water  in  the  kettle  is  pushed 
away  by  the  colder,  denser  water  and  rises.     This  process 
is  continued  until  the  liquid  at  the  top  as  well  as  at  the 
bottom  has  reached  the  boiling  point. 

In  convection,  there  is  a  downward  movement  of  the 
colder  liquid  or  air  and  an  upward  movement  of  the  warmer. 
The  air  of  a  room  is  always  warmer  near  the  ceiling  than 
near  the  floor. 

78.  Radiation.  —  Besides    conduction    of    heat    through 
matter  in  contact  with  a  source  of  heat,  and  convection  in 
currents  of  liquids  and  gases,  there  is  another  method  by 


76        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

which  heat  is  distributed  more  rapidly  and  through  greater 
distances.  Heat  passes  through  air  and  some  other  sub- 
stances in  straight  lines  in  every  direction.  This  is  radiation. 
It  is  by  this  method  that  heat  passes  from  the  sun  to  the 


FIG.  32.  —  HOUSE  HEATING  BY  HOT  WATER 

1.  Why  does  water  rise  from  a  heater  in  the  basement  to  the  second 
floor?  2.  Why  is  it  rising  in  one  part  and  falling  in  another,  in  the  radiator 
at  the  left?  3.  Make  a  diagram  like  the  right-hand  radiator;  connect  it 
properly  with  the  rest  of  the  system  and  indicate  the  direction  of  hot  and 
cool  water  currents. 

earth  and  to  other  planets;   and  from  stoves,  radiators,  and 
lamps  to  objects  around  them. 

If  this  radiated  heat  falls  upon  a  body  through  which  it 
cannot  pass,  it  is  absorbed  and  the  temperature  of  the  body 
rises.  The  sun's  radiations  pass  through  the  air,  with  very 
little  absorption,  to  the  earth,  which  absorbs  the  heat  and  is 
warmed  by  it. 


HEAT:    DISTRIBUTION  AND  MEASUREMENT         77 

79.  How  the  Air  is  Warmed.  —  The  air  in  contact  with 
a  stove   is   warmed   by   conduction.     Being   lighter,  it  is 
pushed  away  by  cooler  air  and  moves  upward  (convection) . 
In  a  similar  way,  the  atmosphere  surrounding  the  earth  is 
warmed  by  heat  from  the  earth.     Besides  distributing  heat 
by   conduction   and   convection,    the   earth   radiates   heat. 
This  radiated  heat  passes  through  the  air,  if  it  is  dry,  without 
raising  its  temperature;    but  if  there  is  much  vapor  in  the 
air,  the  vapor  prevents  the  passage  of  radiated  heat  and  the 
air  retains  the  heat.     A  layer  of  cloud  near  the  earth  at 
night  is  like  a  blanket  keeping  the  earth  warm. 

80.  Intensity  of  Heat. — The  intensity  of  heat  is  stated  in 
terms  of  degrees  of  a  thermometer.     Water,  oil,  air,  and  iron 
at  a  given  degree  (as  at  10°  C.  or  50°  F.)  have  the  same 
temperature  or  intensity  of  heat. 

Very  high  temperatures  cannot  be  measured  with  an  in- 
strument made  of  glass  because  the  glass  would  melt,  but 
they  are  sometimes  determined  by  the  amount  of  expansion 
of  a  metal  rod.  For  such  measurements,  a  rod  is  fastened 
at  one  end  to  a  frame,  and  the  other  end  is  supported  but 
free  to  move.  As  the  rod  becomes  heated,  it  lengthens  and 
pushes  against  a  movable  pointer.  This  pointer  indicates, 
on  a  scale,  the  increase  in  temperature.  Such  small  differ- 
ences as  degrees  are  not  indicated,  but  a  change  of  a  hundred 
degrees  or  more  is  shown.  Red-hot  iron 'has  a  temperature 
of  1,000°  F. 

81.  Quantity    of    Heat.  —  A  teacupful  of  water  and  a 
pailful    may  have    the  same  temperature,   but  the  larger 
amount  of  water  would  have  the  greater  quantity  of  heat. 
It  would  melt  a  greater  weight  of  ice  or  raise  the  temperature 
of  a  larger  mass  of  matter  a  given  number  of  degrees. 

82.  The  Calorie. —  The  metric  unit  used  in  measuring  the 
quantity  of  heat  in  a  body  is  called  the  calorie.    It  is  the 
quantity  of  heat  required  to  warm  one  gram  of  water  through 
one  degree  Centigrade.     For  example,  to  warm  one  gram  of 


78        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

water  from  15°  C.  to  25°  C.  requires  10  calories;  to  warm 
50  grams  of  water  from  30°  C.  to  100°  C.  requires  50  X  70 
or  3,500  calories.  A  body  in  cooling  gives  out  heat.  A 
gram  of  water  in  cooling  one  degree'  Centigrade  gives  out 
one  calorie. 

83.  The    Quantity   of   Heat  Absorbed   by   Water.  —  If 
equal  weights  of  water,  copper,  and  mercury  are  warmed 
through  the  same  number  of  degrees,  very  unlike  amounts  of 
heat  energy  are  required.     The  quantity  of  heat  required  to 
raise  the  temperature  of  a  pound  of  water  one  degree  will 
warm  a  pound  of  copper  ten  degrees  or  a  pound  of  mercury 
about  thirty  degrees.     That  is,  one  tenth  as  many  calories 
are  required  to  warm  a  pound  of  copper  one  degree,  and  one 
thirtieth  as  many  to  warm  a  pound  of  mercury  one  degree, 
as  to  warm  a  pound  of  water  a  single  degree.     No  solid, 
and  no  other  liquid,  absorbs  so  much  heat  in  a  given  rise 
of    temperature   as  water   does.     (LABORATORY   MANUAL, 
Exercise  XI.) 

84.  Influence    of    Bodies    of    Water   upon    Climate.  — 
Water  has  a  much  greater  quantity  of  heat  to  distribute 
to  objects  around  it  than  other  substances  at  the  same  tem- 
perature,  because  it  absorbs    more    heat    than    the  other 
substances  do,  while  gaining  the  same  number  of  degrees. 
Water  is  not  so  good  a  conductor  of  heat  as  metals,  rocks, 
or  other  solids,  and  for  this  reason  does  not  distribute  its 
heat  so  rapidly  to  the  surrounding  air.     As  it  is  commonly 
expressed,  "  water  keeps  warm  longer." 

These  facts  have  a  very  important  bearing  on  the  sub- 
ject of  the  climate  of  islands  and  of  land  near  a  large  lake 
or  an  ocean. 

A  great  lake  or  an  ocean,  having  been  slowly  heated 
through  the  summer  to  a  temperature  of  75°  F.  or  24°  C., 
has  a  great  quantity  of  heat  to  transfer  and  will  do  it  slowly. 
The  land  loses  heat  rapidly  after  sunset,  but  near  a  lake  or 
ocean  the  air  receives  heat  from  the  water  during  the  night 


HEAT:    DISTRIBUTION  AND  MEASUREMENT         79 

and  so  does  not  have  a  freezing  temperature  when  the 
ground  does.  This  delays  the  season  of  frost  in  the  fall  at 
places  near  the  water.  Grapes  and  other  fruits  which  ripen 
late  are  more  successfully  grown  near  the  lakes  in  New  York 
State  than  at  a  distance  from  them. 

85.  Heat  and  Energy.  —  Heat  is  a  form  of  energy;  it 
can  do  work.  As  the  temperature  of  a  body  rises,  its  mole- 
cules vibrate  more  rapidly  and,  in  so  doing,  separate  farther 
apart;  that  is,  the  volume  of  the  body  is  increased.  Thus 
pressure  is  exerted  upon  surfaces  in  contact  with  the  body. 


FIG.  33.  —  THE  STEAM  CHEST  OF  AN  ENGINE 

In  the  left-hand  figure,  steam  is  shown  entering  from  the  boiler  at  B, 
passing  through  D  to  the  cylinder.  It  exerts  pressure  on  P,  pushing  it  to 
the  end  of  the  cylinder.  Steam  passes  out  through  C  and  O  to  the  con- 
denser. The  valve  rod  VR  is  moved  by  other  machinery  so  as  to  close  the 
entrance  to  D  when  the  cylinder  is  filled  with  steam.  C  is  then  open  to 
S.  Trace  the  path  of  the  steam  from  B  to  O  in  the  right-hand  figure. 

When  water  is  changed  to  steam,  the  vapor,  if  unconfined, 
occupies  about  1700  times  as  much  space  as  the  liquid  did. 
The  force  of  this  expansion  is  used  to  exert  a  push  on  the 
piston  in  the  cylinder  of  an  engine.  When  the  steam  is 
admitted  first  into  one  end  of  the  cylinder  and  then  into  the 
other,  the  piston  is  pushed  back  and  forth.  By  means  of 
a  connecting  rod,  other  parts  of  the  machinery  are  kept  in 
motion. 


80        FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 

The  use  of  steam  for  this  kind  of  work  about  the  year  1770 
was  the  beginning  of  great  progress  in  rapid  travel  on  land 
and  sea  and  in  the  manufacture  of  cloth,  tools,  and  food. 
Electric  power  has  recently  displaced'  steam  in  many  kinds 
of  work;  but  unless  natural  water  power  is  available,  steam 
is  still  relied  upon  to  turn  the  machinery  that  is  necessary  to 
make  electric  currents. 

EXERCISES 

1.  Describe  changes  in  the  physical  state  of  matter  produced  by 
changes  in  temperature. 

2.  Why  does  the  mercury  rise  in  the  tube  of  a  thermometer  when 
you  put  your  finger  on  the  bulb?     How  could  you  make  it  fall  con- 
siderably in  a  short  time? 

3.  How  many  Fahrenheit  degrees  are  there  between  the  freezing 
and  boiling  points  of  water?     How  many  Centigrade  degrees? 

4.  Which  shows  a  greater  change  of  temperature,  one  Fahrenheit 
degree  or  one  Centigrade  degree?     State  the  arithmetical  relation  be- 
tween the  value  of  a  Centigrade  degree  and  a  Fahrenheit  degree. 

5.  How  many  degrees  above  0°  F.  is  9P  above  freezing?     How 
many  degrees  above  0°  C.  is  5°  above  freezing?     Which  is  the  higher 
temperature?     Why? 

6.  Show  why  32  is  added  in  one  case  and  subtracted  in  the  second 
case,  in  changing  the  readings  of  one  thermometer  scale  to  the  other. 
(See  §  75.) 

7.  68°  F.  is  a  comfortable  house  temperature.     What  is  the  equiva- 
lent in  degrees  Centigrade? 

8.  Which  is  the  greater  rise  in  temperature,  from  32°  F.  to  50°  F. 
or  from  0°  C.  to  12°  C.?     Prove  your  answer. 

9.  (a)  Which  has  the  higher  temperature,   1,000  g.  of  water  at 
40°  C.  or  500  g.  at  82°  C.? 

(6)  Which  has  the  greater  amount  of  heat,  1000  g.  of  mercury 
or  500  g.  of  water  at  the  same  temperature.  Explain.  Give  the 
answer  in  calories. 

10.  Why  is  there  greater  probability  of  a  frost  on  a  clear  night  than 
on  a  cloudy  night? 


CHAPTER  VI 
LIQUIDS  AND   THEIR  PROPERTIES 

86.  Properties    of    Liquids.  —  The  special  characteristics 
of  liquids  are: 

Mobility,  or  freedom  to  change  form,  as  liquids  do  when 
poured  from  a  pitcher  into  a  cup. 

Incompressibility,  or  resistance  to  pressure  which  tends  to 
reduce  the  bulk.  A  bottle,  when  full  of  water,  may  be 
burst  by  putting  in  a  cork. 

Viscosity,  or  tendency  of  the  particles  to  cling  together. 
The  form  of  a  drop  is  due  to  viscosity. 

Volatility,  or  tendency  to  change  to  a  vapor.  Ether  on 
the 'skin  disappears  very  quickly. 

Water,  the  most  familiar  liquid,  is  used  as  a  standard 
in  comparison  of  liquids.  Alcohol  is  less  dense  and  more 
volatile  than  water;  tar  is  a  very  viscous  liquid;  molasses, 
while  less  viscous  than  tar,  is  more  so  than  water.  All 
liquids  are  practically  incompressible. 

87.  Hydraulic   Presses    and   Elevators.  —  We  make  use 
of  the  incompressibility  and  mobility  of  liquids  in  running 
certain    machines,    like    presses    and    elevators.      In   both 
presses  and  elevators,  a  platform  is  placed  upon  a  piston 
or  plunger  in  a  water-tight  cylinder.    Water  is  forced  into 
the  cylinder,  and  as  the  water  pushes  up  the  plunger,  the 
platform  rises.     In  the  press,  the  object  to  be  compressed  is 
placed  upon  the  platform,  which  moves  up  until  it  meets 
an    immovable    surface.     Great   pressure    is    then  exerted 
against  the  substance  on  the  platform.     Bundles  of  cotton, 
hay,  or  paper  are  thus  made  into  compact  bales. 

81 


82        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

Passenger  elevators  are  constructed  with  a  strong  cage  or 
frame-work  above  the  platform.  When  the  operator  stops 
the  elevator,  he  closes  a  valve  so  as  to  prevent  more  water 
coming  into  the  cylinder.  When  the  'elevator  descends,  he 
opens  a  valve  and  allows  water  to  escape  from  the  cylinder; 


FIG.  34.- — A  HYDRAULIC  PRESS 

1.  By  means  of  a  small  pump  p,  water  is  forced  from  i  through  t,  into 
the  cylinder  i'.  The  pressure  exerted  by  one  square  inch  of  the  surface 
of  the  piston  p  is  transmitted  to  each  square  inch  of  the  surface  of  p' '.  If  the 
pressure  of  p  is  25  Ib.  and  pf  is  100  times  the  area  of  p,  what  is  the  pres- 
sure upon  pr?  2.  Why  does  not  p'  sink  back  after  being  pushed  up?  In  a 
passenger  elevator,  the  valves  V  and  V  are  opened  or  closed  by  the  operator 
in  the  elevator.  3.  Learn  from  a  dictionary  the  meaning  of  hydraulic. 

the  elevator  then  descends  by  gravity,  checked  by  the  resist- 
ance of  the  water  as  it  moves  slowly  out  of  the  cylinder. 

88.  Solution.  —  Liquids  have  the  power  of  dissolving 
other  substances,  that  is,  of  absorbing  particles  of  other 
substances  between  their  molecules.  The  absorbed  solid, 
liquid,  or  gas  disappears  and  the  result  is  a  liquid  mixture 
called  a  solution.  The  solution  may  have  a  different  taste, 
odor,  or  color  from  the  original  liquid,  which  is  known  as 


LIQUIDS  AND  THEIR  PROPERTIES  83 

the  solvent.  The  substance  has  dissolved  and  is  thus  shown 
to  be  soluble. 

Water  is  a  solvent  for  many  substances,  but  not  for  others, 
such  as  fat,  wax,  and  gum.  Alcohol  dissolves  many  solids 
which  are  not  soluble  in  water.  Benzine  is  another 
solvent.  It  is  their  ability  to  dissolve  grease,  gums,  and 
such  substances  that  makes  alcohol  and  benzine  useful  as 
cleansers. 

Metals  are  not  soluble  in  water  or  in  alcohol,  but  dis- 
appear after  a  time  in  acids.  In  such  a  case  the  product  is 
not  a  mixture,  as  in  the  case  of  sugar  and  water,  but  a  new 
compound.  If  a  solution  of  sugar  and  water  is  boiled  until 
the  water  has  all  evaporated,  sugar  will  remain  in  solid  form. 
But  the  liquid  formed  by  the  action  of  the  acid  upon  the 
metal,  on  being  evaporated,  will  not  leave  the  original  metal 
but  a  very  different  solid  in  the  form  of  crystals. 

89.  Natural  Waters.  —  Raindrops  are  nearly  pure  water; 
but  while  the  rain  water  soaks  through  the  ground,  various 
minerals  become  dissolved  in  it.  These  minerals  in  very  small 
quantities  are  found  in  the  water  of  wells,  springs,  and  rivers. 
Water  also  dissolves  gases  and  some  organic  matter  from  the 
ground.  Many  of  these  dissolved  impurities  are  harmless, 
but  some  are  sources  of  disease.  It  is  best,  therefore,  not 
to  drink  well-water  or  brook-water  which  has  passed  near 
houses  and  barns.  Such  water  can  be  made  safe  for  drinking 
by  boiling  it  for  ten  minutes  or  more  and  then  cooling  it. 
Injurious  organisms,  such  as  disease  germs,  are  destroyed  by 
long  continued  heat. 

Natural  waters  are  not  pure,  though  they  may  be  harm- 
less. Nearly  pure  water  can  be  obtained  by  distilling  the 
water  of  springs,  rivers,  and  even  the  sea.  The  dissolved 
mineral  matter  does  not  vaporize  but  remains  as  a  solid 
after  all  the  water  has  evaporated.  The  distillate  may 
contain  some  of  the  gases  which  were  dissolved  in  the 
water,  and  so  it  is  not  perfectly  pure. 


84        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

90.  Mineral   Springs   and    Salt   Lakes.  —  Many  springs 
contain  dissolved  mineral  matter  in  sufficient  quantities  to 
be  detected  by  the  taste.     Some  mineral  springs  are  medicinal 
in  character  and  their  water  is  recommended  by  physicians 
in  the  treatment  of  some  diseases.     It  does  not  follow,  how- 
ever, that  these  waters  are  beneficial  to  every  one. 

Salt  lakes,  which  contain  dissolved  salt  and  other  minerals, 
are  found  in  dry  regions  where  evaporation  goes  on  rapidly. 
Pure  water  is  continually  evaporating  from  the  lakes,  while 
streams  are  constantly  bringing  in  minerals  in  solution. 
When  such  lakes  have  no  outlet,  they  become  more  and 
more  salt. 

91.  Gravity,    the    Cause    of    Streams.  —  Water,  like  all 
other  matter,  has  weight;  that  is,  it  is  attracted  by  the  earth. 
Hence,  unless  restrained,  it  falls  to  the  lowest  possible  level. 
This  falling,  due  to  gravity,  is  the  cause  of  flowing  water 
in  streams.     The  water  seems  to  slide  or  roll  along  over 
the  surface  of  the  earth,  but  in  reality  streams  fall,  some  a 
few  feet  in  a  mile  of  their  course,  others  hundreds  of  feet. 
Rapids,  cascades,  and  waterfalls  are  names  given  to  parts 
of  a  stream  wher.e  the  fall  is  considerable  within  a  short 
distance. 

The  headwaters  of  the  Connecticut  River  are  nearly  a 
thousand  feet  above  sea  level,  so  in  its  journey  of  four  hun- 
dred miles  to  the  sea  the  water  falls  one  thousand  feet.  In 
a  few  places  the  fall  is  twenty  or  more  feet  at  one  place  and 
there  the  energy  of  the  falling  mass  is  utilized  in  turning 
machinery. 

92.  Water  Power.  —  Long  before  steam  was  used  to  run 
machinery,  men  placed  large  water  wheels  where  the  water 
could  fall  upon  them,  turning  them  as  it  fell.     Connected 
with  these  wheels  was  the  machinery  to  grind  grain,  to  saw 
logs,  and  later  to  weave  cloth.     At  the  present  time  water 
is  used  to  run  dynamos,  which  are  machines  for  producing 
the  electric    currents  that  furnish  both   light    and   power. 


LIQUIDS  AND  THEIR  PROPERTIES 


85 


The  trolley  cars  of  many  cities  are  run,  lighted,  and  warmed 
by  the  energy  of  waterfalls  in  distant  rivers. 

93.  Springs  and  Wells.  —  Since  water  seeks  low  places, 
the  rain  which  falls  upon  the  earth  flows  c)own  a  slope,  or 
settles  into  the  soil  and  finds  its  way  lower  still  through 
porous  rocks  or  through  cracks.  When  the  water  reaches  a 
layer  of  rock  through  which  it  cannot  pass,  it  may  follow 
the  rock  to  some  place  where  the  layer  comes  to  the  surface, 


FIG.  35.  —  POWER  FROM  FALLING  WATER 

Water  flows  from  some  height  through  the  sluiceway  into  a  bucket 
on  the  water  wheel.  1.  Suppose  that  the  buckets  are  empty  and  the  wheel 
is  at  rest;  water  enters  the  bucket  nearest  to  s.  What  force  sets  the  wheel 
in  motion?  2.  Why  does  the  wheel  move  faster  when  two  buckets  are  filled? 
3.  Why  is  this  form  of  bucket  better  than  one  with  straight  boards? 

perhaps  many  miles  from  where  the  water  started.     Many 
hillside  springs  are  formed  in  this  way. 

A  stratum  of  porous  rock  often  contains  much  water.  If 
the  rock  is  inclined,  as  in  a  hilly  region,  some  parts  of  the 
stratum  are  much  lower  than  the  source  of  the  water.  From 
the  lower  levels,  water  rises  through  fissures,  or  cracks,  to  the 
surface  of  the  ground,  by  pressure  of  the  water  behind  it. 
Such  springs  are  fissure  springs.  They  bring  water  often 
from  a  great  distance  as  well  as  from  a  great  depth. 


86        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

By  digging  or  drilling  to  the  underground  water-level,  it 
is  possible  to  bring  water  to  the  surface  by  its  own  pressure 
or  by  pumps.  Wells  of  one  or  the  other  of  these  types 
furnish  water  for  domestic  and  agricultural  purposes  in 
many  districts. 

Many  springs  and  wells  have  a  uniformly  cool  temperature 
at  all  seasons.  This  is  because  the  absorption  and  radiation 
of  heat  by  the  earth  change  the  temperature  for  only  a  short 


FIG.  36.  —  FISSURE  SPRING  AND  WELL 

If  i  is  a  layer  impervious  to  water,  the  water  which  has  passed  through 
the  porous  layers  (p)  must  rest  there,  or  follow  down  the  inclined  layer  i. 
A  fissure  through  the  upper  layers  may  deliver  the  water  at  s.  1.  Why  is 
such  a  spring  usually  a  "bubbling"  spring?  2.  If  a  tube  were  sunk  there, 
how  high  might  the  water  rise  in  it?  (Make  no  allowance  for  friction.) 
3.  Would  making  a  well  at  w  have  any  effect  upon  the  spring?  4.  Is  there 
any  better  place  for  a  well?  Why? 

distance  below  the  surface.  The  cooler  the  water  of  a  spring 
is  in  summer,  the  deeper  one  would  have  to  go  to  find  its 
supply. 

94.  Pressure  in  Liquids.  —  As  a  diver  descends  below 
the  surface  of  water,  he  is  conscious  of  a  pressure  which 
steadily  increases  with  the  depth.  If  he  is  to  remain  some 
time  below  the  surface,  he  puts  on  a  loosely  fitting  rubber 
suit,  provided  with  a  metal  helmet  and  a  rubber  tube  through 
which  air  can  be  forced  down  to  him  from  above.  It  is 
necessary  to  force  the  air  down  for  two  reasons:  first,  to 


LIQUIDS  AND  THEIR  PROPERTIES 


87 


supply  the  diver  with  oxygen  for  his  lungs;  and  second,  to 
overcome  the  pressure  exerted  by  the  water  against  his  suit. 
For  example,  if  the  diver  is  working  at  a  depth  of  seventy 
feet  under  water,  the  pressure  upon  his  body  is  about  three 


FIG.  37.  —  A  DIVER  PREPARING  TO  GO  INTO  THE  WATER 

On  his  shoulders  the  diver  carries  a  cylinder  of  compressed  air  con- 
nected by  a  tube  with  a  machine  for  supplying  the  air.  What  pressure  is 
there  upon  every  sq.  dm.  of  his  body  at  100  dm.  depth? 

times  as  much  as  at  the  surface.  As  long  as  he  is  provided 
with  air  at  a  pressure  sufficient  to  balance  the  pressure  of 
the  water,  his  suit  will  fit  loosely.  A  greater  pressure  of  air 
will  tend  to  burst  the  suit;  a  smaller  pressure  will  allow  it 


88        FIRST  YEAR   COURSE   IN   GENERAL  SCIENCE 


to  collapse  and  press  against  his  body.     As  fast  as  the  diver 

uses  the  air,  it  escapes  through  a  valve  into  the  water,  fresh 

ai^  being  pumped  to  him  all  the  while. 

95.   Laws  of  Pressure  in  Liquids.  —  Experiments  prove 

three  things  about  the  pressure  of  liquids: 

First,  that  the  pressure  varies  directly  with  the  depth.      The 

pressure  of  the  water  upon  a  body  ten  feet  below  the  surface 
is  twice  as  great  as  upon  a  body  five 
feet  below. 

Second,  that  the  pressure  varies 
with  the  density  of  the  liquid.  The 
pressure  upon  a  body  ten  feet  below 
the  surface  of  the  ocean  is  greater  than 
upon  a  body  ten  feet  below  the  surface 
of  a  pond,  because  the  salt  water  of 
the  ocean  is  more  dense  than  the  fresh 
water  of  the  pond. 

Third,  that  at  any  given  point  in 
the  liquid  the  pressure  is  the  same  in 
all  directions.  At  any  point  upon  a 
body  under  water,  there  is  the  same 
pressure  from  above,  below,  and  from 
each  side. 

98.  Direction  of  Pressure.  —  Pres- 
sure in  a  liquid  is  exerted  at  right 
angles  to  the  surface  of  the  body  upon 
which  it  is  acting.  Suppose  a  cubical 
block,  two  centimeters  on  each  edge, 
is  placed  under  water  so  that  its  top 
is  three  centimeters  below  the  surface 
of  the  water.  The  bottom  of  the 

block  is  five  centimeters  below  the  surface  and  the  average 

depth  of  each  side  is  four  centimeters. 

In  accordance  with  the  first  law  of  pressure  in  liquids,  the 

pressure  on  all  six  sides  can  be  found.      The  total  downward 


FIG.  38.  —  PRESSURE 
UPON  A  SUBMERGED 
BODY 

1.  Which  is  greater, 
the  upward  or  the  down- 
ward pressure  upon  this 
block?  2.  Would  the 
block  remain  (naturally) 
in  this  position:  (a)  if  its 
density  were  greater  than 
that  of  water?  (6)  if  it 
were  less?  (c)  if  it  were 
the  same  as  that  of  water? 

3.  Give    the   reasons   for 
one     of     these     answers. 

4.  Explain     from     these 
answers  why  a  body  ap- 
parently   weighs    less    in 
water  than  in  air. 


LIQUIDS  AND  THEIR  PROPERTIES 


89 


pressure  upon  the  top  is  equal  to  the  weight  of  (2X2X3) 
12  cubic  centimeters  of  water.  The  total  upward  pressure 
on  the  bottom  of  the  block  is  equal  to  the  weight  of 
(2  X  2  X  5)  20  cubic  centi- 
meters of  water.  The  total 
pressure  upon  each  side 
of  the  block  is  equal  to  the 
weight  of  (2X2X4)  16 
cubic  centimeters  of  water . 
The  third  law  of  pres- 
sure is  applied  in  the 
construction  of  hydraulic 
presses  and  elevators. 
Water  enters,  or  is 
pumped  into,  the  small 
cylinder  with  a  force,  for 
example,  of  100  grams  to 
the  square  centimeter  of 
area.  The  water  at  the 
bottom  of  this  cylinder 
has  that  pressure  upon  it. 
Because  the  pressure  is 
exerted  in  every  direction, 
the  water  at  the  same 
level  in  the  large  cylinder 
receives  a  pressure  of  100 
grams  to  the  square  centi- 
meter. This  pressure,  in 
turn,  is  exerted  upward 
as  well  as  horizontally 
upon  the  water  and  upon 
each  square  centimeter  of  3-  Fr°m  which 

stove?     4.    Trace 

the  piston  in  the  large 
cylinder.  If  the  area  of 
the  large  piston  is  900 


FIG.  39.  —  GRAVITY  PRESSURE   IN   A 
HOT-WATER  BOILER 


1.  Under  what  conditions  is  an 
elevated  water  tank  necessary  to  a  hot- 
water  system?  2.  If  a  tank  is  not  needed, 
where  does  the  water  enter  the  boiler? 

does  {i  etnteT  ^e 

its  course  from  the 
water-front  of  the  stove  to  a  story  above 
the  boiler.  5.  Name  in  order  the  changes 
of  direction  of  pressure  from  the  street 
to  the  stove.  (Use  upward,  horizontal.) 


90        FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 


100  Ib. 


square  centimeters,  the  total  upward  effect  will  be  a  pressure 
of  900 X  100  grams. 

97.  Buoyancy  in  Liquids.  —  Careful  study  of  the  dia- 
gram (Fig.  38)  will  show  that  the  horizontal  pressures  on 
opposite  sides  of  the  submerged  block  are  equal,  but 

are  acting  in  opposite  directions, 
1  Ib,  so  that  the  block  will  not  tend  to 
move  in  either  direction  sidewise. 
But  as  the  upward  pressure  upon 
the  bottom  of  the  block  is  greater 
than  the  downward  pressure  on 
the  top,  the  block  will  be  buoyed 
up  in  the  liquid  by  a  force  equal 
to  the  difference  between  the  up- 
ward and  downward  pressures. 
This  is  the  reason  that  a  body 
seems  to  lose  weight  in  water; 
part  of  its  weight  is  supported 
by  upward  pressure  of  the 
liquid. 

98.  Capillarity.  —  If  water  is 
put  into  a  glass,  it  is  seen  to  rise 
a  little  higher  where  it  touches  the 
glass  than  elsewhere  at  the  sur- 
face. If  a  glass  tube  is  placed 
upright  in  water,  the  water  stands 
higher  in  the  tube  than  around  it. 
This  rise  of  liquids  in  tubes,  or  on 
the  side  of  a  solid  placed  in  the 
liquid,  is  called  capillarity.  It  is 
due  to  the  attraction  of  the  solid 
for  the  liquid. 

Capillarity  can  be  shown  with  all  liquids  which  wet - 
that  is,  adhere  to  a  solid.     Mercury  does  not  adhere  to  glass; 
it  will  roll  off  from  clean  glass  and  leave  no  trace.     Mercury 


FIG.  40. — TRANSMISSION  OF 
PRESSURE 

1.  The  area  of  the  piston 
p  is  1  sq.  in.;  what  is  the 
pressure  exerted  upon  the  sur- 
face of  the  water  beneath? 
2.  This  pressure  is  transmitted 
in  every  direction:  what  is 
the  pressure  in  the  horizontal 
tube?  3.  In  what  direction  is 
pressure  exerted  in  the  large 
cylinder?  4.  What  is  the 
pressure  upon  each  square 
inch  of  P?  5.  From  the 
weights  indicated  here,  what 
must  be  the  area  of  P?  6.  If 
more  weights  were  placed 
upon  p,  and  it  went  down  1 
in.,  would  Prise  1  in.?  Why? 


LIQUIDS    AND   THEIR    PROPERTIES 


91 


does  not  rise  higher  in  tubes  than  in  the  surrounding  liquid, 
as  water  does,  but  is  slightly  depressed. 

Small  spaces  between  threads  close  together,  as  in  a  wick 
or  cloth,  have  the  effect  of 
tubes  in  which  liquid  rises. 
If  a  dry  cloth  is  placed  with 
one  end  in  water,  the  liquid 
rises  in  the  spaces,  as  in 
tubes,  and  the  cloth  is 
soon  dampened  throughout. 
Water  sometimes  rises 
through  the  cloth  over  the 
edge  of  a  bowl  and  drops 
from  the  other  end  of  the 
cloth.  Kerosene  rises  be- 
tween and  upon  the  threads 
of  the  lamp  wick  to  the  top, 
where  it  burns.  Blotting 
paper  takes  up  ink  be- 
tween the  fibers  of  the 
paper.  In  plants,  capillar- 
ity aids  in  the  rise  of  liquids 
from  the  roots  through  the 


FIG.  41.  —  CAPILLARITY 


The  smaller  the  bore  of  a  tube, 
the  higher  a  liquid  will  rise  by  capil- 
larity. The  diameter  of  the  tube 
shown  here  is  2  mm.,  which  is  much 
larger  than  that  of  many  plant  cells. 
Liquids  pass  from  cell  to  cell  by 
osmosis,  and  rise  in  the  cell  by 
capillarity. 


stems  to  the  leaves.      In  soil, 

it  aids  in  the  rise  of  water  from  lower  levels  to  the  surface 

of  the  ground. 

EXERCISES 

1.  Which  would  be  likely  to  furnish  cooler  water,  a  hillside  spring 
or  a  fissure  spring?     Why? 

2.  At  what  depth  in  fresh  water  will  the  pressure  be  75  g.  per  square 
centimeter? 

3.  Why  is  pressure  in  the  ocean  greater  than  at  the  same  depth  in 
a  pond? 

4.  Which  apparently  loses  more  weight,  a  body  partially  immersed 
in  water  or  a  body  wholly  immersed?     Why? 

60   A  cubical  block  5  cm.  on  each  edge  is  immersed  in  water  to  a 


92       FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

depth  of  25  cm.  above  the  top  of  the  block.  State  (a)  the  depth  of  the 
bottom  of  the  block;  (6)  the  average  depth  of  each  side;  (c)  the  pres- 
sure in  grams  on  the  top;  (d)  the  pressure  in  grams  on  the  bottom; 
(e)  the  pressure  in  grams  on  each  side;  (/)  the  difference  in  pressure  on 
the  bottom  and  the  top.  Illustrate  by  a  diagram. 

6.  (a)  How  many  cubic  centimeters  of  water  are  displaced  by  the 
block  described  in  Ex.  5?     (6)  Compare  this  with  the  answer  to  Ex.  5,  /. 

7.  If  the  block  described  in  Ex.  5  weighs  280  g.  in  air,  what  is  its 
weight  in  water? 

8.  •  If  the  downward  pressure  on  the  tube  admitting  water  to  the 
cylinder  of  an  elevator  is  100  Ib.  to  the  square  inch,  what  will  be  the 
upward  pressure  on  the  large  piston,  if  it  is  one  square  foot  in  area? 

9.  Why  is  it  easier  to  float  in  salt  water  than  in  fresh  water? 

10.  Why  is  a  cloth  better  than  a  newspaper  to  wipe  up  water? 

11.  Describe  the  surface  of  good  blotting  paper  and  tell  why  such 
a  surface  is  required. 


CHAPTER  VII 

PROPERTIES  OF  GASES;  THE  ATMOSPHERE;  ATMOSPHERIC 

PRESSURE 

99.  Properties    of    Gases.  —  Since  gases  are  a  form  of 
matter,  they  have  weight  and  occupy  space.     Some  gases 
are  elements,  such  as  oxygen,  hydrogen,  and  nitrogen.     Some 
are  compounds,  as  ammonia  and  carbon  dioxide.     Some  are 
mixtures,  as  illuminating  gas  and  air. 

Gases  have  some  of  the  same  physical  properties  as  solids 
and  liquids,  but  in  different  degrees.  The  special  proper- 
ties of  expansibility  and  compressibility  belong  to  gases  in 
a  greater  degree  than  to  solids  or  liquids.  A  cubic  foot  of 
air  on  being  heated  becomes  more  than  a  cubic  foot,  although 
its  weight  remains  the  same.  By  pressure  it  can  be  made  to 
occupy  much  less  than  a  cubic  foot  of  space,  but  its  weight  is 
still  the  same.  If  some  gas  is  removed  from  a  vessel  con- 
taining one  cubic  foot,  the  weight  of  the  remaining  gas  is 
diminished,  but  it  expands  to  fill  the  space  and  its  volume  is 
still  one  cubic  foot. 

100.  Molecular  Motion.  —  The  expansibility  of  gases  is 
a  result  of  the  action  of  molecules.     The  molecules  of  gases, 
as  well  as  of  other  bodies,  are  in  very  rapid  vibration.     As 
they  strike  one  another,  they  rebound  and  thus  set  other 
particles  in  more  rapid  vibration  and  are  separated  farther 
and  farther.     They  strike  the  walls  of  the  vessel  that  con- 
tains the  gas,  and  if  the  space  is  enlarged,  or  an  opening 
is  made,  the  gas  expands  to  fill  the  larger  space  or  finds  its 
way  out. 

101.  Solubility   of   Gases.  —  Many  gases  will  dissolve  in 
water  and  remain  more  or  less  permanently  dissolved,  ac- 

93 


94       FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

cording  to  conditions  of  temperature  and  pressure.  What 
is  commonly  called  "  ammonia"  is  the  gas  ammonia  dissolved 
in  water.  Air  dissolves  in  water  and  in  this  way  the  oxygen 
necessary  to  life  is  furnished  to  fishes  and  other  water  ani- 
mals. If  a  tumbler  of  drinking  water  is  left  standing  for 
a  time,  small  bubbles  may  be  seen  clinging  to  the  inside  of 
the  glass.  These  bubbles  contain  air,  and  the  water  is  not  so 
agreeable  to  drink  as  it  was  before  the  air  left  it.  All  natural 


FIG.  42. — SOLUTION 
OF  AIR  IN  WATER 


FIG.  43.  —  DIFFUSION  OF 

GASES 


FIG.  42.  The  water  here  represented  has  been  growing  warmer  while 
standing  for  some  hours.  Air  which  was  dissolved  in  the  water  has  sepa- 
rated and  appears  as  bubbles  on  the  glass.  1.  What  did  the  change  of 
temperature  have  to  do  with  the  change  in  the  water?  2.  How  does  air 
become  dissolved  in  water? 

FIG.  43.  One  of  these  flasks  contains  an  invisible  acid  gas  dissolved 
in  water;  the  other  contains  invisible  ammonia  gas,  also  in  solution.  If 
these  two  gases  come  together,  they  form  a  new  compound  in  the  form  of  a 
fine  white  solid.  1.  What  shows  that  they  have  diffused?  2.  Suppose  that 
one  of  the  bottles  were  removed;  what  change  would  occur? 

waters  contain  dissolved  air,  and  much  spring  water  contains 
the  gas  carbon  dioxide.  If  water  is  heated,  the  dissolved 
air  and  other  gases  expand  and  escape.  Such  water  tastes 
stale  or  flat,  even  after  it  is  cooled. 

102.  Soda  and  Carbonated  Waters.  —  Large  quantities 
of  carbon  dioxide  dissolved  in  water  give  the  pungent, 
slightly  acid  taste  familiar  in  plain  soda  water.  The  name 
"soda  water"  was  given  because  the  carbon  dioxide  was 


PROPERTIES  OF  GASES  95 

formerly  prepared  from  soda,  but  there  is  really  no  soda  in 
soda  water.  The  tanks  containing  soda  water  are  made  of 
metal  and  are  very  strong.  They  are  partially  filled  with 
water,  and  carbon  dioxide  is  then  forced  into  the  water  with 
great  pressure.  As  long  as  the  tank  is  closed,  the  gas  re- 
mains dissolved  in  the  water.  If  the  valve  is  opened,  the 
gas  escapes  with  violence,  bringing  with  it  a  little  water  in 
the  form  of  a  spray. 

There  are  many  manufactured  liquids,  called  by  the  names 
of  celebrated  medicinal  springs,  which  contain  carbon  dioxide. 
Minerals  are  dissolved  in  the  water  and  then  carbon  dioxide 
is  added.  The  waters  are  much  more  agreeable  to  the 
taste  after  they  are  " charged"  with  the  gas.  Such  waters 
are  called  "carbonated"  and  are  close  imitations  of  natural 
waters. 

A  great  number  of  "soft  drinks"  owe  their  effervescence 
to  compressed  carbon  dioxide. 

103.  Diffusion.  —  Gases  are  soluble  in  other  gases.     This 
dissolving  of  one  gas  in  another  is  usually  spoken  of  as  mix- 
ing or  diffusion.     If  ammonia  gas  escapes  from  a  bottle  of 
ammonia  solution  or  from  ammonia  smelling  salts,  its  odor 
is  soon  evident  to  a  person  some  distance  away.     The  gas 
has  been  dissolved  in  the  air  and  has  spread  quickly.     Some 
gases  diffuse  more  rapidly  than  others;  diffusion  is  assisted 
by  movement  of  the  air. 

Diffusion  of  gases,  and  also  of  liquids,  occurs  even  when 
they  are  separated  by  a  thin  membrane  of  plant  or  animal 
tissue.  Diffusion  through  a  membrane  is  called  osmosis. 
It  plays  a  very  important  part  in  the  distribution  of  gases 
and  liquids  in  living  bodies.  Oxygen  from  the  air  we  inhale 
passes,  by  osmosis,  through  the  membranes  of  the  lungs  into 
the  blood  vessels,  to  be  carried  to  all  parts  of  the  body. 

104.  The     Pressure     of     the     Air.  —  The  atmosphere, 
which  envelops  the  whole  earth  and  moves  with  it  as  it 
rotates,  is  held  in  place,   like  other  movable  bodies,   by 


96        FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 


gravity.  The  pressure  of  the  air  due  to  its  weight  is 
nearly  fifteen  pounds  on  a  square  inch  of  surface  at  sea 
level.  This  means  that  the  column  of  air  directly  above 
this  square  inch  of  surface  would  weigh  about  fifteen 
pounds. 

As  one  rises  to  higher  levels  and  leaves  some  of  the  air 
beneath,  the  pressure  becomes  less.     One  of  the  ways  of 

I!  "   i!  4 


3ft. 


FIG.  44.  —  DENSITY  OF  THE  AIR  AT  DIFFERENT  ELEVATIONS 

1.  What  is  the  reason  that  the  air  is  more  dense  at  sea  level  than  at 
high  elevations?  2.  What  is  the  density  of  the  air  at  the  highest  mountain 
known  (about  5^  mi.  high)?  3.  Why  would  the  mercury  stand  at  1  in.  at 
a  height  of  15  mi.? 

determining  the  altitude  of  a  mountain  is  by  measuring  the 
pressure  of  the  atmosphere.  Scientists  estimate  that  there 
is  some  atmosphere  at  a  height  of  two  hundred  miles,  but 


PROPERTIES  OF  GASES 


97 


at  that  height  it  exerts  very  little  pressure.     About  half  the 

weight  of  all  the  air  is  within  three  miles  of  the  earth.     This 

is  because  the  lower  part  of  the  atmosphere,  having  the 

weight  of  all  the  upper  air 

resting  upon  it,  is  compressed 

and  therefore    has    greater 

density. 

105.  The  Barometer.  - 
An  instrument  for  measuring 
the  pressure  of  the  air  is 
called  a  barometer.  In  a 
simple  form,  it  consists  of  a 
glass  tube  about  three  feet 
long  closed  at  one  end;  the 
tube  contains  mercury  and 
stands  inverted  m  a  cup  of 
mercury.  The  mercury  in 
the  tube  stands  at  the  height 
of  about  thirty  inches  above 
the  level  of  the  mercury  in 
the  cup. 

As  the  tube  is  open  at 
the  bottom,  the  mercury 
is  free  to  leave  it,  but  does 

not  do  SO  because  the  air 
is  pressing  down  Upon  the 
mercury  in  the  CUp.  The 

pressure   is   transmitted 

,  1 

through    the    liquid    both     height  of  only  30  in.?    3.  Suppose  that 

horizontally    and    upwards,    both  ends  were  open;  why  would  the 

mercury  not  remain  in  the  tube? 

and  thus   the  downward 

pressure  of  the  air  holds  the  column  of  mercury  in  the 

tube. 

We  know  that  the  weight  of  thirty  inches  of  mercury  in 
a  tube  one  square  inch  in  area  is  nearly  fifteen  pounds.     The 


FIG.  45.  —  TORRICELLI'S 
EXPERIMENT 

In  1643  an  Italian  named  Tor- 
ricelli  observed,  in  using  apparatus 
like  this,  that  mercury  would  remain 
in  a  closed  tube  to  the  height  of  30  in. 
if  the  tube  were  inverted  with  the 
open  end  in  mercury.  1.  He  dis- 
covered the  reason.  What  is  it? 
2.  Why  will  the  mercury  remain  at  the 


98        FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

downward  pressure  of  the  air  which  supports  this  column  of 
mercury  must  be  equal  to  the  weight  of  the  column  — 
that  is,  nearly  fifteen  pounds  on  a  square  inch. 

A  complete  barometer,  which  is  to  be  carried  from  place 
to  place,  is  provided  with  a  metal  case  to  protect  the 
glass  and  to  keep  the  tube  upright.  At  the  back  of  the 
tube  is  a  scale  of  inches,  or  centimeters,  by  which  to  read 
the  height  of  the  mercury  column. 

At  sea  level  the  world  over,  under  ordinary  conditions, 
the  height  of  the  mercury  in  the  tube  of  a  barometer  is 
29.9  inches,  or  76  centimeters,  above  the  surface  of  the 
mercury  in  the  cup.  In  ascending  to  higher  elevations,  a 
fall  of  one  inch  is  observed  during  the  first  900  feet,  but 
in  an  ascent  of  two  miles  the  fall  of  mercury  averages  one 
inch  for  every  1,000  feet  of  ascent.  Leadville,  Col.,  is 
10,600  feet  above  sea  level;  its  barometer  reading  under 
ordinary  conditions  is  about  20  inches. 

106.  Differences   in   Air   Pressure.  —  If  at  sea  level  the 
mercury  in  a  barometer  is  higher  than  76  centimeters,  the 
pressure  of  the  air  is  greater  than  under  ordinary  conditions. 
If  the  barometer  reading  is  lower  than  76  centimeters,  the 
pressure  is  below  the  normal.     These  differences  in  air  pres- 
sure are  due  to  one,  or  both,  of  two  causes:  variation  in  the 
amount  of  water  vapor  in  the  air,  and  variation  in  the  tem- 
perature.    To  illustrate:   if  the  temperatures  are  the  same, 
a  cubic  foot  of  dry  air  has  a  greater  density,  and  therefore  a 
greater  pressure,  than  a  cubic  foot  of  moist  air.     If  the 
moisture  is  the  same,  a  cubic  foot  of  cold  air  has  a  greater 
density,  and  therefore  a  greater  pressure,  than  a  cubic  foot 
of  warm  air.     These  two  conditions  may  counteract  each 
other  or  they  may  tend  to  produce  the  same  effect  on  the 
barometer,  sending  the  mercury  up  or  down. 

107.  Pressure  upon  our  Bodies.  —  We  are  not  conscious 
of  the  weight  of  the  atmosphere  because  there  is  equal  pres- 
sure on  all  sides  of  the  body.     We  are  not  crushed  by  this 


PROPERTIES  OF  GASES 


99 


pressure  because  of  the  elasticity  of  the  fluids  of  the  body, 
which  exert  a  similar  outward  pressure.  When  travelers 
rapidly  ascend  mountains  of  great  height,  or  airmen  reach 
high  levels  in  the  air,  blood  sometimes  bursts  through  the 
thin  membranes  of  the  nose  and  eyes.  This  is  because 
the  pressure  outside  the  body  has  diminished  while  the 


FIG.  46.  —  AN  AIR  PUMP 

A  receiver  (r)  fits  closely  upon  a  metal  plate.  A  tube  (£)  connects 
the  space  in  the  receiver  with  the  cylinder  of  the  pump.  When  the  piston 
(p)  is  lifted,  the  space  c  is  enlarged  and  air  moves  into  it  from  r,  equalizing 
the  pressure.  When  the  piston  goes  down,  V  closes  and  V  opens  and 
allows  air  to  pass  through.  A  part  of  the  air  originally  in  the  receiver  is 
removed.  A  gauge  (g)  connected  with  t  shows'  that  the  pressure  in  the 
receiver  is  now  less  than  normal.  1.  If  one  half  of  the  air  of  the  receiver 
is  removed  by  one  double  stroke  of  the  piston,  how  much  of  the  original 
amount  will  be  left  after  two  such  strokes?  2.  How  much  after  four  strokes? 

internal  pressure  has  not  had  time  to  change  during  the 
rapid  ascent. 

108.  The  Air  Pump.  —  The  air  pump  is  a  machine  for 
taking  air  out  of  a  closed  space,  in  somewhat  the  same 
way  that  water  is  pumped  from  a  well.  An  inverted  jar, 
called  the  receiver,  is  placed  upon  a  brass  plate,  which  has 
an  opening  into  a  tube  connected  with  the  cylinder  of  the 
pump.  The  receiver  fits  the  plate  air-tight,  and  at  each 


100      FIRST  YEAR   COURSE   IN   GENERAL  SCIENCE 


stroke  of  the  piston  a  portion  of  the  air  in  the  receiver  is 

removed. 

A  space  from  which  all  air  has  been  removed  is  a  vacuum. 

With  an  air  pump  it  is   impossible  to  produce  a  perfect 

vacuum,  but  from  experiments 
with  a  partial  vacuum  much 
can  be  learned  about  the  be- 
... .1     havior  of  the  atmosphere. 

109.  The  Direction  of 
Atmospheric  Pressure.  —  It 
is  easy  to  understand,  without 
an  experiment,  that  air  exerts 
pressure  downward,  because 
all  matter  has  weight.  The 
air  pump  makes  it  possible  to 
show  that  air  also  exerts  pres- 
sure upward  and  in  a  hori- 
zontal direction .  Suppose 
that  a  thin  sheet  of  rubber  is 
tied  closely  over  the  mouth 
of  a  bottle  filled  with  air. 
The  molecules  of  air  in  the 
bottle  are  in  the  same  rapid 
motion  as  those  outside,  and 
the  rubber  remains  flat,  be- 
cause the  pressure  above  and 
below  it  is  the  same. 

If  now  the  bottle  is  placed 
under  the  receiver  of  an  air 
pump,  and  some  of  the  air 
is  removed  from  around  the 
bottle,  the  rubber  bulges  up- 
ward. The  air  in  the  bottle 
is  pressing  in  every  direction, 
but  the  rubber  is  the  only 


FIG.  47. — APPARATUS  TO  BE  USED 
WITH  AN  AIR  PUMP 

1.  The  glass  dish  A  is  placed 
on  the  plate  of  an  air  pump  and 
one  double  stroke  of  the  piston  is 
made.  What  is  the  effect  on  the 
rubber  cover?  Why?  2.  What  is 
the  effect  of  continued  pumping? 
3.  If  B  is  placed  on  the  plate  while 
the  mercury  is  at  1,  and  the  pump 
is  worked,  the  mercury  falls  to  2  in 
the  tube.  Explain  its  position  at 
1,  and  at  2. 


PROPERTIES   OF   GASES- 


101 


1 


part  that  can  show  the  pressure.  When  air  is  allowed  to  go 
back  into  the  receiver,  the  rubber  becomes  flat  again.  If  the 
bottle  is  placed  in  a  horizontal  position  and  the  experiment 
is  repeated,  the  rubber  bulges  out  in  a  horizontal  direction. 

The  laws  of  pressure  in 
gases  are  similar  to  those  in 
regard  to  liquids. 

110.  Relation  between 
the  Pressure  and  the  Volume 
of  a  Gas.  —  Gases  are  very 
compressible  and  highly 
elastic.  If  pressure  is  ap- 
plied to  compress  a  gas  into 
a  smaller  volume  and  is  then 
removed,  the  gas  returns  to 
its  original  volume.  As  it 
expands,  the  gas  may  be 
made  to  do  work,  by  push- 
ing back  the  body  that 
compressed  it.  Air  guns, 
air  springs  for  closing  doors, 
air  brakes,  and  other  devices 
make  use  of  the  energy  of 
compressed  air. 

When  a  gas  has  been 
compressed  into  half  the 
space  it  originally  occupied, 

it  exerts  twice  as  great  pressure  as  before  compression.  This 
relation  between  the  volume  and  the  pressure  of  a  confined 
gas  continues  as  long  as  the  substance  remains  a  gas.  Under 
a  very  great  compressing  force  at  low  temperature,  gases 
—  even  air  —  become  liquids. 

Steam  at  high  temperature  in  a  confined  space  exerts  hun- 
dreds of  pounds  of  pressure  to  the  square  inch.  This  pressure 
does  an  immense  amount  of  useful  work  if  properly  controlled 


FIG.   48.  —  RELATION    BETWEEN 
PRESSURE  AND  VOLUME  OF  GASES 

1.  What  is  the  pressure  upon  the 
mercury  in  the  long  arm  of  the  left 
tube?  2.  What  shows  that  the 
downward  pressure  of  the  gas  in  the 
space  a  is  equal  to  the  downward 
pressure  in  the  long  arm  of  the  tube? 

3.  How  great  is  the  downward  pressure 
in  the  long  arm  of  the  second  tube? 

4.  Why  has  the  volume  of  the  gas  in 
a'  decreased?     5.  How  much  pressure 
does  the  gas  in  of  now  exert? 


102      FIRST  YE4R   COURSE  IN   GENERAL  SCIENCE 


and  directed,  and  great  destructive  work  otherwise.  When 
the  steam  boiler  in  a  factory  bursts,  parts  of  the  boiler  are 
sometimes  thrown  against  the  walls  of  the  building,  knocking 
down  the  walls  and  often  causing  loss  of  life. 

In  the  process  of  "charging"  the  steel  cylinder  from  which 
the  tank  of  a  soda  fountain  is  filled,  a  very  great  amount  of 

compressed  carbon  dioxide  is 
forced  into  it.  A  cylinder  that 
holds  five  gallons  at  ordinary 
pressure  may  have  forty  gallons 
of  gas  forced  into  it.  This 
makes  a  pressure  of  one  hundred 
and  twenty  pounds  on  each 
square  inch  of  the  inside  of  the 
cylinder,  while  on  the  outside 
the  pressure  of  the  air  is  only 
fifteen  pounds.  If  there  is  a 
defect  in  the  metal,  this  tremen- 
dous inside  pressure  may  cause 
an  explosion  of  the  cylinder. 

111.  The  Siphon. — A  siphon 
is  a  tube  in  the  shape  of  an 
inverted  U  but  with  unequal 
arms.  It  may  be  made  of  glass 
or  of  rubber  or  some  other 


FIG.  49.  —  SIPHONS 

The  figure  represents  a  jar 
of  liquid  with  sediment  in  the 
bottom  and  two  siphons.  The 
short  arm  of  b  is  the  vertical  dis- 
tance sb.  The  long  arm  of  6  is 
the  vertical  distance  be.  1. 
Which  is  the  short  arm  of  a? 
2.  What  is  its  length?  3.  Under 
what  condition  will  the  liquid 
stop  flowing  through  b?  4. 
Through  af  5.  Which  siphon 
will  remove  more  water?  6.  Why 
is  b  the  better  one  to  use  in  this 
case? 


flexible  material.  It  is  used  to  carry  liquids  from  a  higher 
to  a  lower  level  over  an  elevation,  as  in  transferring  from 
one  tank  or  barrel  to  another.  One  advantage  in  its  use 
is  that  sediment  in  the  bottom  of  the  tank  need  not  be 
disturbed  during  the  removal  of  the  liquid. 

To  set  a  liquid  flowing  through  a  siphon,  the  air  must  first 
be  removed  from  the  tube.  To  do  this,  fill  the  tube  with 
the  liquid  or  with  water,  then  cover  both  ends  and  invert  the 
tube.  Place  the  shorter  arm  in  the  liquid  to  be  transferred 
and  the  long  arm  over  the  vessel  which  is  to  receive  the 


PROPERTIES   OF    GASES 


103 


liquid.  The  end  of  the  long  arm  must  be  lower  than  the 
surface  of  the  liquid  that  is  to  be  moved.  When  the  ends 
of  the  siphon  are  uncovered,  liquid  falls  from  the  long  arm. 
This  would  tend  to  cause  a  vacuum  above,  but  the  pressure 
of  air  upon  the  surface  of  the  liquid  causes  it  to  rise  in  the 
short  arm,  as  soon  as  the  pressure  is  lessened  at  the  other 
end.  The  flow  continues  until  the  liquid  reaches  the  same 
level  on  both  sides,  or  until  the  surface  of  the  liquid  is  as 
low  as  the  end  of  the  short  arm  of  the  siphon. 

112.  Pumps.  —  We  are  all  familiar  with  the  operation  of 
taking  lemonade  through  a  straw.  We  say  we  "suck  it  up." 
What  we  do  is  to  draw  the  air  from  the  tube,  creating  there 
a  partial  vacuum.  (An  old  saying  is  that  "Nature  abhors 
a  vacuum."  This  means  that  in  natural  conditions  a  vacuum 
does  not  exist.)  Just  as  soon  as 
the  pressure  is  diminished  in  the 
tube,  the  pressure  of  air  upon 
the  liquid  pushes  it  up  through 
the  tube  to  the  mouth.  If  air 
is  allowed  to  come  into  the  top 
of  the  tube  for  an  instant,  the 
liquid  falls  back  into  the  glass. 

This  method  of  drawing 
lemonade  from  a  glass  is  similar 
to  the  method  used  in  drawing 
water  from  a  well  by  a  pump 
which  is  sometimes  called  the 
suction  pump.  This  consists  of 
a  pipe  of  metal  or  wood  placed 
upright,  with  the  lower  end  near 

the  bottom  of  the  well.  A  piston  works  up  and  down  in  the 
upper  and  larger  part  of  the  pipe  (called  the  cylinder) ,  fitting 
it  water-tight.  An  opening  through  the  piston  is  closed  by 
a  hinged  cover,  (called  a  valve)  which  opens  upward.  There 
is  also  a  valve  opening  upward  in  the  pipe  below  the  piston. 


FIG.  50.  —  A  PEN  FILLER 

1.  Compare  the  situation  in 
A  with  the  first  step  in  the 
process  of  sucking  liquid  through 
a  straw.  2.  Compare  B  with 
the  next  step.  3.  Under  what 
conditions  would  ink  rise  to  the 
top  of  the  tube? 


104      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


By  means  of  a  handle  attached  to  the  piston  rod,  the  piston 
is  raised  and  lowered.  As  the  piston  goes  down,  the  air  in 
the  cylinder  pushes  up  through  the  yalve  in  the  piston, 
while  the  valve  in  the  pipe  below  remains  closed  by  its 
own  weight.  Conditions  in  the  cylinder  are  now  just  as  at 
first,  except  that  the  piston  is  as  far  down  as  the  length  of 
its  rod  allows.  There  is  air  above  and  below  the  piston. 


FIG.  51. — THE  LIFT  PUMP 


FIG.  52. —  THE  FORCE  PUMP 


FIG.  51. —  This  diagram  shows  the  essential  parts  of  a  common  lift  pump. 

1.  What  relation  must  there  always  be  between  the  area  of  the  piston  and 
the  cylinder?     2.  In  what  direction  does  the  piston  valve  open?     3.  What 
opens  it  on  the  first  downward  motion  of  the  piston?     4.  Why  is  30  ft.  the 
greatest  practicable  distance  between  the  surface  of  the  well  and  the  valve 
in  the  pipe? 

FIG.  52. —  1.  Why  is  there  no  valve  in  the  piston  of  a  force  pump? 

2.  Why,  if  there  were  no  air  chamber,  would  water  be  delivered  in  spurts 
from  the  side  of  the  cylinder?     3.  For  what  use  is  a  constant  stream  neces- 
sary?    4.  In  Fig.  52,  what  shows  that  the  air  in  the  chamber  is  compressed? 

The  water  in  the  lower  end  of  the  pipe  is  at  the  same  level 
as  the  water  in  the  well. 

When  the  piston  is  raised,  its  valve  remains  closed  by  its 
own  weight  and  pressure  of  the  air  above.  As  the  piston 
rises,  the  air  space  beneath  becomes  larger  and  therefore 
the  pressure  of  the  air  within  this  space  is  decreased.  The 
air  in  the  pipe  below,  at  the  same  pressure  as  that  outside, 


PROPERTIES    OF    GASES  105 

pushes  open  the  valve  and  enters  the  cylinder.  The  pres- 
sure on  the  water  in  the  pipe  is  thus  decreased,  and  water 
is  pushed  farther  up  in  the  pipe,  by  the  air  pressure  on 
the  surface  of  the  water  in  the  well.  Atmospheric  pres- 
sure, which  must  be  depended  on  to  push  the  water  from 
the  well  through  the  pipe  into  the  cylinder,  can  sustain  a 
column  of  water  about  30  feet  high.  The  distance,  there- 
fore ,  between  the  surface  of  the  water  in  the  well  and  the 
bottom  of  the  cylinder  must  not  be  more  than  30  feet. 

When  after  several  strokes  the  water  has  reached  the 
cylinder,  if  the  piston  is  pushed  down,  the  water  presses 
the  valve  in  the  piston  open  and' passes  above  it.  The  water 
is  then  lifted  to  the  outlet,  by  few  or  many  strokes,  accord- 
ing to  the  length  of  the  cylinder. 

The  suction  pump  or,  as  it  is  better  named,  the  lift  pump 
is  used,  not  only  to  raise  water  from  wells  and  cisterns,  but 
to  remove  gasoline  and  kerosene  from  barrels  and  tanks, 
to  pump  out  sea  water  which  has  leaked  into  the  hold  of 
a  ship,  to  pump  river  and  lake  water  for  use  in  factories, 
and  for  many  other  similar  purposes. 

113.  The  Force  Pump.  —  There  are  two  important  differ- 
ences between  a  lift  pump  and  a  force  pump.  The  force 
pump  has  no  valve  in  the  piston,  and  it  has  an  opening 
near  the  bottom  of  the  cylinder,  into  a  .tube,  out  of  which 
the  water  is  forced  to  levels  much  higher  than  the  pump. 
Water  is  raised  from  a  cistern  or  well  to  the  bottom  of  the 
cylinder  by  atmospheric  pressure,  just  as  it  is  in  the  lift 
pump.  It  is  then  forced  out  of  the  exit  tube  by  pressure 
of  the  solid  piston  in  its  down  stroke.  The  water  is  thus 
sent  out  in  a  spurt,  through  the  exit  tube,  with  every 
stroke  of  the  piston. 

In  order  to  furnish  a  steady  stream  and  to  avoid  succes- 
sive shocks  to  the  pipe,  the  force  pump  of  a  fire  engine  is 
provided  with  an  air  chamber  through  which  the  water 
passes  from  the  cylinder.  Here  the  water  compresses  the 


106      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

air,  as  it  enters  the  chamber  faster  than  it  can  go  out. 
While  the  piston  is  lifted  for  another  stroke,  the  elastic  air 
expands  and  forces  out  the  remaining  water,  thus  giving  a 
moderately  steady  stream. 

In  parts  of  the  country  where  there  are  no  elevated 
regions,  many  towns  and  cities  have  their  water  supply  in 
lakes  or  rivers  lower  than  some  sections  of  the  town. 
Such  places  have  a  pumping  station  where  machine-power 
pumps  work  constantly  to  fill  elevated  reservoirs  or  stand- 
pipes  and  privately  owned  tanks.  From  these  the  water 
is  delivered  under  pressure  to  buildings  and  fire  hydrants. 
Both  lift  pumps  and  force  pumps  may  be  worked  by  wind- 
mills or  gas  engines. 

EXERCISES 

1.  Explain  the  difficulty  of  filling  an  "  empty  "  bottle  held  in  a 
stream  of  water. 

2.  Why  is  a  bottle  still  full  of  air  when  some  of  it  has  been  removed? 

3.  Why  is  there  physical  discomfort  at  high  elevations? 

4.  In  an  inverted  closed  tube,  water  is  supported  by  atmospheric 
pressure  to  a  height  of  34  ft.;  mercury,  to  a  height  of  30  in.     Why  is 
the  mercury  column  shorter?     What  is  the  relation  of  the  density  of 
mercury  to  that  of  water,  as  shown  by  this  fact? 

6.  A  vertical  open  tube  40  in.  long  is  placed  with  its  lower  end  in 
a  cup  of  mercury,  and  its  upper  end  is  connected  with  an  air  pump. 
If  some  of  the  air  is  removed  from  the  tube,  what  will  happen?  Give 
the  reason. 

6.  What  adjective  is  commonly  applied  to  air  under  more  than 
ordinary  pressure?     How  is  it  used? 

7.  A  mass  of  gas  under  ordinary  atmospheric  pressure  occupies 
3,000  cu.  cm.     How  many  cubic  centimeters  will  there  be,  if  the  pressure 
is  doubled?     If  halved? 

8.  Will  a  balloon  filled  with   gas  expand  or  contract  as  it  rises? 

9.  Explain  how  the  height  of  a  mountain  can  be  calculated  from 
barometric  readings. 

10.  How  many  meters  high  is  a  mountain,  if  the  barometric  readings 
at  the  same  time  at  top  and  bottom  are  564  mm.  and  754  mm.  respec- 
tively? (A  fall  of  1  mm.  corresponds  to  an  ascent  of  12  m.) 

11.  If  the  mercury  in  a  barometer  stands  at  76  cm.  at  sea  level, 
what  would  be  the  length  of  a  column  at  an  elevation  of  3  miles? 


CHAPTER  VIII 
WEATHER;  WINDS  AND   STORMS;  CLIMATE 

114.  Variations  in  the  Composition  of  the  Atmosphere. 

The  only  way  in  which  the  composition  of  the  air  varies 
is  in  the  amount  of  water  vapor  it  contains.  The  air  con- 
tains nitrogen,  oxygen,  and  carbon  dioxide  in  practically  the 
same  proportion  everywhere  and  all  the  time.  Water  vapor 
is  present  in  varying  quantities,  according  to  the  location. 
The  air  is  never  without  water  vapor  even  in  deserts. 

It  is  therefore  more  correct  to  speak  of  the  humidity  — 
that  is,  moisture  —  than  of  the  dryness  of  the  air.  The  air 
is  said  to  be  saturated  when,  at  a  given  temperature,  there 
is  as  much  vapor  in  the  air  as  it  can  hold  at  that  temperature. 
The  higher  the  temperature,  the  more  vapor  the  air  is  able 
to  hold.  If  the  air  contains  T%  as  much  vapor  as  would 
saturate  it,  its  condition  is  expressed  as  relative  humidity 
60  per  cent,  which  means  that  it  contains  60  per  cent  as 
much  vapor  as  there  could  be  at  that  temperature. 

When  the  relative  humidity  is  high,  if  the  air  is  cooled, 
a  part  of  the  vapor  is  condensed  and  rain  falls,  or  dew  is 
deposited.  Blades  of  grass  cool  earlier  in  the  evening  than 
stones  or  earth;  therefore  the  vapor  is  condensed  upon  the 
grass  first.  Dew  is  often  seen  on  the  outside  of  a  pitcher  of 
ice  water.  The  cold  pitcher  cools  the  surrounding  air  to 
the  temperature  at  which  dew  is  deposited  —  the  dew  point. 
This  is  not  a  uniform  temperature  like  the  freezing  point, 
but  varies  with  the  relative  humidity. 

Change  in  relative  humidity  and  change  in  temperature 
are  the  two  principal  causes  of  change  in  the  pressure  of  the 
atmosphere.  Cold,  dry  air  is  of  the  greatest  density  and 

107 


108      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

therefore  highest  pressure.     Warm,  saturated  air  is  of  the 
least  density  and  lowest  pressure. 

115.  Weather.  —  The  condition  of  the  atmosphere  as  re- 
gards temperature,   humidity,   and  motion  determines  the 
weather.     "  Cold,  dry,  and  windy  "  may  describe  the  weather 
of  one  day.     "Warm,  moist,  and  still"  would  describe  the 
other  extreme.     (LABORATORY  MANUAL,  Exercise  XII.) 

116.  The     Weather    Bureau.  —  The  conditions  of  tem- 
perature and  wind  are  of  such  great  importance  to  farming 
and  navigation  that  the  United  States  government  has  es- 


FIG.  53.  —  INSTRUMENTS  USED  BY  THE  UNITED  STATES  WEATHER 

BUREAU 

At  the  left  are  self-registering  thermometers,  which  show  the  maximum 
and  minimum  temperatures  since  they  were  last  adjusted.  Below  is  a 
thermograph,  which  records,  by  a  pen  upon  a  slowly  revolving  paper  cylinder, 
the  changes  in  temperature  during  24  hours. 

In  the  center  is  an  anemometer  to  measure  the  velocity  of  the  \\liid. 
The  cups  are  exposed  in  an  elevated  place  and  their  revolutions,  as  they 
catch  the  wind,  are  recorded  by  a  mechanism  similar  to  that  of  a  gas  meter. 

At  the  right  is  a  self-registering  barometer,  a  barograph. 

Which  one  of  these  instruments  would  give  practically  the  same  record 
in  the  house  as  out  of  doors?  Why? 

tablished  a  Weather  Bureau  as  a  division  of  the  Department 
of  Agriculture.  A  central  office  at  Washington  receives, 
three  times  a  day,  reports  of  the  weather  from  more  than 
a  hundred  stations  scattered  over  the  country.  These 
reports  include  the  degree  of  cloudiness,  direction  and 


WEATHER;    WINDS  AND  STORMS;    CLIMATE      109 

rate  of  the  wind,  humidity,  amount  of  rainfall,  and  the 
readings  of  thermometer  and  barometer.  Men  of  experi- 
ence interpret  the  reports  and  make  up  forecasts  of  the 
weather  for  the  next  twenty-four  hours  or  more.  By  long 
study  it  has  been  learned  that  weather  conditions  follow 
certain  rules  and  move  in  regular  paths  across  the  country. 
Consequently,  from  the  conditions  of  the  atmosphere  to-day 
experts  can  predict  what  will  probably  result  to-morrow. 

The  forecasts  of  the  Weather  Bureau  are  telegraphed  to 
all  sections  of  the  United  States  and  are  reported  by  daily 
papers  and  by  weather  maps  and  cards  posted  in  public 
places.  The  advantages  in  making  use  of  such  information 
can  scarcely  be  estimated.  Farmers  and  sailors,  especially, 
may  take  precautions  which  greatly  reduce  the  dangers  from 
a  sudden  fall  in  temperature  or  from  high  winds.  For  in- 
stance, if  a  frost  is  predicted,  a  farmer  may  often  save  the 
delicate  buds  on  his  young  fruit  trees  by  the  use  of  small 
kerosene  heaters  placed  at  frequent  intervals  in  his  orchard. 
A  few  dollars'  worth  of  kerosene  may  thus  save  thousands 
of  dollars'  worth  of  fruit.  Masters  of  sailing  vessels,  too, 
may  often  escape  danger  to  life  and  property  by  remaining 
in  port  when  storms  have  been  predicted. 

117.  Weather  Records.  —  The  records  of  the  Weather 
Bureau  extend  over  only  about  fifty  years,  but  in  that  short 
time  statistics  of  great  importance  have  been  secured.  Many 
people  have  records  of  the  weather  in  their  own  locality  for 
a  longer  period.  Observations  that  were  recorded  at  the 
time  they  were  made  are  the  only  reliable  information  as  to 
weather  in  the  past. 

From  such  records  it  is  possible  to  learn  the  average 
amount  of  rainfall  and  the  ave'rage  number  of  days  of  sun- 
shine for  ten  or  twenty  years.  This  average  gives  a  stand- 
ard by  which  to  judge  the  weather  of  any  particular  year. 
By  such  standards  only  can  it  be  determined  whether  a 
season  was  a  " remarkably  hot  summer"  or  a  "very  rainy 


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112      FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 

spring."  Our  memories  of  the  weather  often  mislead  us, 
for  the  impression  made  upon  our  minds  by  one  hot  week 
or  many  days  of  rain  is  likely  to  be  recalled  as  describing  a 
whole  season. 

118.  Wind.  —  Wind   is   air  in  motion.     Its  strength  is 
designated  by  different  expressions,  such  as  light  or  stiff 
breeze,  if  the  velocity  is  from  two  to  ten  miles  an  hour; 
strong  wind,  twenty  to  thirty  miles;    gale,  forty  to  sixty 
miles;  and  tornado,  one  hundred  to  two  hundred  miles. 

All  winds  result  from  the  same  condition,  though  the  con- 
dition may  have  different  causes.  This  one  condition  is  the 
difference  in  pressure  of  the  atmosphere  over  adjacent  regions. 

Just  as  water  always  moves  down  hill  in  obedience  to 
gravity,  so  air  moves  out  from  a  region  of  high  pressure  to 
one  of  lower  pressure.  If  over  New  York  State  and  the 
Province  of  Ontario  the  barometer  indicates  a  pressure  of 
30.2  inches  (or  768  mm.),  while  over  New  England  the  pres- 
sure is  29.7  inches  (or  755  mm.),  the  air  moves  toward  New 
England  and  it  is  called  a  west  wind.  The  greater  the 
difference  in  pressure,  the  stronger  the  wind. 

119.  Cyclonic  Movements.  —  If  the  low-pressure  area  is 
surrounded  by  areas  of  higher  pressure,  the  air  moves  in 
from  all  directions,  and  the  currents,  as  they  meet,  unite 
in  an  upward  whirling  motion.     This  is  called  a  cyclone. 
It  may  vary  in  violence  from  a  dust  whirl  in  the  street  to  a 
destructive  gale. 

120.  Constant    Winds.  —  There  are  certain  parts  of  the 
world  where  winds  blow  all  the  time  in  the  same  direction. 
The  air  in  the  equatorial  belt  is  warmer  than  the  air  north 
or  south  of  it  and  contains  much  vapor,  on  account  of  the 
great  extent  of  ocean  there.     For  these  reasons,  air  in  this 
belt  is  lighter  than  the  air  outside,  and  the  heavier  air  pushes 
its  way  into  the  region  of  lower  pressure.     This   causes 
constant  winds  to  blow  toward  the  equatorial  belt  from  both 
north  and  south. 


WEATHER;    WINDS  AND  STORMS;    CLIMATE       113 

121.  The    Belt    of    Calms.  —  The  heated  air  within  the 
equatorial  belt  rises  slowly  and  its  vapor  condenses  in  the 
cooler,  upper  layers  of  air.     Consequently  there  are  frequent 
rains,  but  not  much  wind,  as  there  is  very  little  horizontal 
motion  of  the  air.     Because  of  this  condition,  the  region  is 
named  the  belt  of  calms. 

During  the  year  the  belt  of  calms  shifts  its  position  north 
and  south  across  the  torrid  zone,  according  as  the  positions 
of  the  sun  and  of  the  region  of  greatest  heat  change.  The 
rainy  season  in  the  torrid  zone  changes  according  to  the 
movements  of  the  belt  of  calms.  It  comes  in  the  northern 
half  of  this  zone  during  the  northern  summer  and  in  the 
southern  half  during  our  winter. 

122.  The   Trade   Winds.  —  If  the  earth  were  stationary, 
the  air  moving  into  the  equatorial  belt  would  give  rise  to 
constant  north  winds  blowing  north  of  the  equator,   and 
south  winds  on  the  other  side.     The  great  velocity  of  rota- 
tion at  the  equator,  however,  gives  the  constant  winds  a 
northeast  and  southeast  direction.     This  is  explained  by  the 
fact  that,  owing  to  the  greater  circumference  at  the  equa- 
tor, the  rotation  of  any  equatorial  point  is  faster  than  that 
of  any  point  north  or  south  of  the  equator.     Hence  the  wind 
that  moves  toward  the  equator  does  not  reach  the  point 
toward  which  it  started,  but  a  point  farther  west.     As  a 
result,  the  wind  in  the  northern  half  of  the  torrid  zone  seems 
to  come  from  the  northeast,  and  in  the  southern  half  from  the 
southeast. 

These  constant  northeast  and  southeast  winds  are  called 
trade  winds  because  of  their  help  to  navigation  and  to 
trade. 

123.  Storms.  —  Though  the  term  storm  is  usually  applied 
only  to  rain  or  snowfall,  any  marked  disturbance  of  the  at- 
mosphere is,  properly,  a  storm.     A  storm  occurs  when  there 
is  a  great  difference  of  pressure  over  different  regions,  and 
the  air  moves  rapidly  from  the  high-pressure  area  to  the  re- 


114      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

gion  of  lower  pressure.  This  disturbance  of  the  atmosphere 
is  often  accompanied  by  a  precipitation  of  rain  or  snow.  As 
the  rain  inconveniences  us  more  than  does  the  wind,  we  often 
make  the  mistake  of  thinking  that  the  precipitation  alone 
constitutes  the  storm. 

If  an  atmospheric  disturbance  prevails  over  a  large  area, 
the  storm  is  said  to  be  general.     Such  storms  are  cyclonic 


FIG.  55.  —  AFTER  A  TORNADO,  OMAHA,  NEBRASKA 

That  the  wind  had  a  whirling  instead  of  a  direct  motion  is  shown  by 
the  position  of  the  beams  of  this  house  with  respect  to  the  foundation. 
The  house  was  lifted  away  from  its  foundation  and  turned,  before  it  dropped 
back. 

storms.  As  the  whirl  moves,  the  wind  may  change  in  di- 
rection and  velocity  and  the  amount  of  precipitation  may 
vary  at  different  places,  but  the  same  general  conditions 
continue  for  hours  or  even  days  and  then  pass  away.  In 
the  eastern  part  of  the  United  States  cyclonic  storms  travel 
generally  in  a  northeast  direction.  Reports  to  the  Weather 


WEATHER;    WINDS  AND  STORMS;    CLIMATE       115 

Bureau,  for  instance,  may  show  that  the  atmospheric  dis- 
turbance occurs  first,  perhaps,  in  the  lower  Mississippi 
Valley,  then  in  the  Ohio  Valley,  then  in  New  York  State, 
and  finally  in  New  England.  It  is  not  so  easy  to  trace  the 
course  of  storms  in  the  western  part  of  the  country.  The 
great  variations  in  altitude  in  that  region  cause  irregulari- 
ties in  pressure  which  modify  the  course  of  the  storms. 
Their  general  direction  is  easterly. 

The  study  of  storms  requires  a  thorough  understanding 
of  barometric  conditions  and  humidity,  as  well  as  the  rela- 
tive position  of  mountains,  plains,  and  oceans.  It  is,  there- 
fore, beyond  the  range  of  an  elementary  course  in  science. 
But  careful  observation  of  changes  in  the  weather  leads,  in 
time,  to  a  good  judgment  in  regard  to  local  probabilities, 
so  that  one  may  learn  to  forecast  the  weather  with  consid- 
erable accuracy,  without  understanding  the  laws  that  govern 
the  changes. 

124.  Tropical  Storms.  —  Violent  storms  called  hurricanes 
sometimes  start  near  the  Gulf  of  Mexico  and  travel  north- 
ward along  the  Atlantic  coast.     These  storms  are  greatly 
feared  because  of  damage  to  shipping.     When  the  Weather 
Bureau  receives  information  of  such  storms,  it  directs  that 
storm  signals  be  displayed,  warning  shipmasters  to  remain  in 
port.     Much  life  and  property  are  saved  by  these  warnings. 

125.  Local  Storms.  —  The  term  local  storm  usually  refers 
to  precipitation  which  occurs  in  a  small  area  and  for  a  short 
time.     Such  storms  generally  follow  a  change  in  temperature. 
After  a  hot  sultry  day,  as  the  air  rises  from  the  heated  sur- 
face of  the  earth,  the  vapor  which  it  contains  may  condense 
rapidly  in  meeting  the  higher,  cool  air.     Rain  may  then  fall 
for  a  few  minutes  or  perhaps  hours. 

If  the  condensation  is  very  rapid,  electricity  may  be  de- 
veloped upon  the  clouds  and  flashes  of  lightning  will  show  its 
passage  through  the  air.  The  thunder  which  follows  has 
the  same  cause  as  the  sound  which  results  from  tearing  a 


116      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

piece  of  paper;   viz.,  the  vibration  of  air  particles  that  have 
been  disturbed. 

After  a  shower,  the  atmosphere  is  usually  free  from 
clouds,  and  hence  the  earth  is  cooled  by  rapid  radiation  of 
heat.  It  is  cooled  also  by  the  evaporation  of  rain  water, 
for  the  heat  required  in  evaporation  is  taken  from  the  sur- 
face of  the  ground.  From  one  or  both  of  these  causes,  it  is 
often  true  that  "a  shower  cools  the  air." 

126.  Climate.  —  Climate  may  be  said  to  be  the  average 
of  weather  for  a  long  series  of  years.     It  is  not  correct  to 
say  that  the  climate  is  much  more  severe  in  a  given  place  this 
year  than  last  year,  for  it  requires  many  years  of  observa- 
tion to  determine  the  climate  of  a  place.     It  could  properly 
be  said  that  a  winter  was  severe  or  a  season    rainy.     A 
drouth  may  prevail  one  year,  but  the  next  year  conditions 
may  be  normal  or  there  may  be  an  excess  of  rain. 

A  single  word  is  not  sufficient  to  describe  climate.  The 
climate  may  be  hot  and  dry  with  certain  prevailing  winds, 
or  cold  and  dry  with  some  other  winds.  It  is  customary 
to  speak  of  an  island  climate,  or  a  coast  or  inland  cli- 
mate, according  to  the  situation  of  a  place,  because  various 
physical  conditions  have  an  important  effect  on  climate. 

Variations  in  temperature,  rainfall,  and  wind  cause  all  the 
differences  in  climate. 

127.  Conditions     Affecting     Temperature.  —  There  are 
three  conditions  which  determine  the  temperature  of  a  place. 
The  first  condition  we  are  accustomed  to  call  "  distance  from 
the  equator,"  as  if  the  equator  were  the  source  of  heat. 
The  source  of  most  of  the  earth's  heat  is,  of  course,  the  sun, 
and  because  of  the  nearly  spherical  shape  of  the  earth  dif- 
ferent latitudes  receive  different  quantities  of  heat.    Where 
the  sun  is  directly  overhead,  as  it  is  somewhere  in  the  torrid 
zone  all  the  time,  every  square  mile  of  the  earth  receives  more 
heat  than  an  equal  area  where  the  rays  are  slanting.      At 
the  tropic  of  Cancer  on  June  21,  the  heat  is  received  ver- 


WEATHER;    WINDS  AND  STORMS;    CLIMATE      117 


tically,  that  is,  at  right  angles  to  the  earth's  surface.  On 
the  same  day  at  the  arctic  circle  heat  is  received  in  slanting 
lines,  at  about  half  of  a  right  angle.  The  same  amount  of 
heat  spreads  over  a  larger  surface  when  it  falls  obliquely 
than  when  it  falls  vertically.  Therefore  any  given  area  at 
the  arctic  circle  receives  less  heat  than  an  equal  area  at  the 
tropic  of  Cancer. 

The  second  condition  affecting  temperature  is  altitude, 
or  the  elevation  of  a  place  above  sea  level.  We  use  sea 
level  as  a  convenient  uniform  basis  from  which  to  reckon 
altitude,  even  though  the  place  considered  may  be  thousands 
of  miles  from  the  sea.  / 

The  farther  one  rises 
above  the  earth,  the  less 
heat  is  found.  This 
is  because  the  earth 
warms  the  air.  A  high 
mountain,  rising  above 
the  great  mass  of  the 
earth,  is  surrounded  by 
cool  layers  of  air.  The 
mountain  receives  less 
heat  and  likewise  gives 
out  less  heat  to  the 
surrounding  air  than 
land  on  the  lower  levels 
of  the  earth. 

The    third    condition 


c  a  o 

FIG.  56.  —  VARIATIONS  IN  THE  AMOUNT 
OF  HEAT  AT  DIFFERENT  LATITUDES 


If  each  vertical  line  represents  the  same 
•number  of  rays  of  heat  as  each  oblique  line, 
then  the  surface  ab  receives  the  same 
amount  of  heat,  as  cb.  1.  Compare  the 
amount  of  heat  received  on  j  of  ab  with 
the  heat  on  an  equal  surface  of  cb.  2.  In 
what  month  does  Cuba  receive  vertical 
rays?  3.  Name  some  part  of  the  world 
upon  which  rays  would  fall  obliquely  (as 
affecting  the  tempera-  on  cb)  in  the  same  month.  4.  In  which  case 

ture  of  a  place  is  near-    would  a  sc*uare  mile  of  the  earth  receive 

,    ,      ,         ,    more  heat? 

ness  to  a  great  body  of 

water.  The  ocean,  or  any  other  large  body  of  water,  absorbs 
more  heat  and  warms  more  slowly  than  the  land  at  the 
same  temperature.  When  the  ocean,  for  instance,  has 
become  warmed  to  80°  F.,  it  has  absorbed  more  heat  than 


118     FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 

the  land  has  absorbed  at  80°.  The  water  also  retains  its 
heat  longer  than  the  land. 

At  the  beginning  of  the  warm  season,  a  large  body  of  water 
remains  for  some  time  cooler  than  the  land,  and  "sea  breezes  " 
temper  the  heat  along  its  shores.  At  the  close  of  the  warm 
season,  on  the  other  hand,  the  sea  or  lake  cools  more  slowly 
than  the  land.  The  general  effect  of  a  large  body  of  water 
is  to  make  the  climate  of  coast  or  island,  both  summer  and 
winter,  less  extreme  than  the  climate  of  the  interior  at  the 
same  latitude.  The  difference  between  the  average  winter 
temperature  and  the  average  summer  temperature  of  a 
coast  or  island  is  smaller  than  the  difference  in  the  interior 
of  a  continent.  The  climate  of  Bermuda  or  Hawaii,  for 
instance,  is  much  more  equable  than  that  of  the  interior  of 
the  United  States  in  the  same  latitudes.  (LABORATORY 
MANUAL,  Exercise  XIII.) 

This  third  condition  — -  nearness  to  the  ocean  —  has  an 
important  relation  to  rainfall,  which  is  another  great  factor 
affecting  climatic  conditions.  The  amount  of  rainfall  is 
largely  dependent  upon  the  direction  of  winds,  whether 
coming  from  an  ocean  or  from  an  arid  region. 

Water  on  the  surface  of  the  ocean  is  constantly  changing 
to  vapor  and  passing  into  the  air.  As  this  vapor-laden  air 
spreads  over  the  continent  and  meets  cooler  air,  or  rises 
over  high  lands,  the  vapor  condenses  and  rain  or  snow  falls. 
Air  from  the  ocean  always  carries  vapor;  the  amount  varies, 
inasmuch  as  cool  air  absorbs  less  vapor  than  warm  air. 
Winds  from  the  desert,  on  the  other  hand,  contain  so  little 
vapor  that  they  bring  no  rain. 

128.  Changes  in  Climate.  —  Elderly  people  sometimes 
remark,  "The  climate  has  changed  since  I  was  young." 
The  climate  is  doubtless  the  same,  but  the  circumstances 
under  which  people  live  and  travel  have  changed  so  greatly 
that  it  is  natural  that  people  should  think  there  have  been 
changes  of  climate. 


WEATHER;    WINDS  AND  STORMS;    CLIMATE      119 

The  history  of  people  who  lived  in  Asia  Minor,  Greece, 
and  Italy  twenty-five  hundred  years  ago  shows  us  that  the 
same  native  fruits,  grains,  and  trees  grew  there  then  as  now; 
that  the  country  people  lived  in  the  same  kind  of  dwellings 
and  wore  the  same  amount  of  clothing  as  to-day;  and  that 
they  raised  flocks  and  herds  of  the  same  domestic  animals 
as  are  raised  now.  It  is  evident  that  the  climate  of  that 
part  of  the  world  has  not  changed  materially  in  over  two 
thousand  years.  It  is  not  likely,  then,  that  the  climate  on 
our  continent  has  changed  within  a  lifetime. 

EXERCISES 

1.  A  pitcher  of  ice  water  at  a  temperature  ,of  40°  becomes  covered 
with  dew  on  a  day  when  the  relative  humidity  is  75  per  cent.     Explain 
why  the  same  effect  is  not  produced  with  water  at  60°. 

2.  An  area  in  Kansas  has,  on  a  given  day,  a  barometric  pressure 
averaging  30.2  in.;    another  area  has  a  pressure  of  29  in.     State  the 
direction  of  air  movement  between  these  regions  and  explain. 

3.  Two  other  regions  have  pressures  of  31  and  29  in.  respectively. 
Compare  the  velocity  of  wind  with  that  in  the  case  of  Ex.  2. 

4.  Why  does  sprinkling  the  streets  and  sidewalks  cool  the  air? 

5.  Describe  the  weather  of  yesterday. 

6.  Describe  the  climate  of  the  state  you  live  in. 

7.  Name  a  distant  state  or  country,  in  about  the  s.ame  latitude  as 
yours,  which  has  a  climate  differing  in  any  respects  from  your  local 
climate.     Tell  what  you  think  is  the  reason  for  the  difference. 

8.  In  what  ways  does  climate  influence  pepple  as  regards  dwellings, 
food,  occupations,  and  material  for  clothing? 


CHAPTER  IX* 
LIGHT 

129.  Sources  of  Light.  —  People  are  now  living  who  can 
remember  when  candles  and  whale-oil  lamps  were  the  ordi- 
nary means  of  lighting  houses  and  streets.     Later  kerosene 
oil  and  gas  came  into  use,  and  now  electricity  is  very  generally 
used  for  lighting  streets,  public  places,  and  houses.     Light 
from  gas,  candles,  and  oil  lamps  is  caused  by  particles  of 
carbon  made  red-hot  in  the  flame.     The  heat  of  the  flame 
is  due  to  combustion  of  gas  and  vapors  from  the  heated 
wax  or  oil.     Thus  the  origin  of  the  light  is  the  heat  of 
combustion.     In  the  case  of  an  electric  lamp,  the  conductor 
is  heated  to  a  glowing  heat  or  incandescence  by  the  resis- 
tance which  is  offered  to  the  current. 

Besides  combustion  and  electricity,  there  is  another  source 
of  light:  friction  between  two  bodies.  Here  it  is  resistance 
to  motion  which  produces  heat.  Often  a  small  particle  of 
metal  or  stone  is  heated  to  light-giving  temperature,  as  when 
a  spark  is  struck  by  a  horse's  shoe  on  the  pavement.  Meteors 
are  made  red-hot  by  the  resistance  of  the  air,  through  which 
they  pass  with  immense  velocity. 

130.  Intensity   of   Light.  —  The  rapid  vibration  of  mole- 
cules, from  whatever  cause,  produces  heat;  and  if  the  vibra- 
tions are  sufficiently  rapid,  heat  causes  the  body  to  become 
incandescent.     The  brightness  or  intensity  of  light  increases 
with  the  temperature  of  the  luminous  body.     The  cause  of 
the  vibrations  is  not  always  known.     This  is  the  case  with 
the  sun  and  the  stars. 

In  stating  the  amount  of  light  given  from  a  luminous  body, 
the  term  candle  power  is  used.  One  candle  power  is  the 

120 


LIGHT  121 

light  given  by  a  sperm  candle  burning  about  8  grams  of  wax 
an  hour.  A  common  type  of  incandescent  electric  light  is 
the  16-candle-power  light,  which  gives  about  as  much  light 
as  16  standard  candles. 

131.  Vision.  —  It  is  often  said  that  we  "see  light/'  but 
that  is  not  strictly  true.     The  fact  is  that  we  see  an  object 
which  gives  light,  or  we  look  into  a  room  which  is  lighted. 
We  see  bodies  which  send  light  to  the  eye. 

Air,  clear  water,  and  glass  are  the  ordinary  mediums 
through  which  light  passes.  Such  substances  are  called 
transparent.  Horn,  celluloid,  and  ground  glass  are  semi- 
transparent  or  translucent.  An  opaque  substance  is  one 
through  which  light  does  not  pass;  as  brick,  wood,  and 
stone. 

132.  Light,   a   Form   of   Energy.  —  Light,  like  heat,  is  a 
form  of  energy,  for  it  does  work,  although  the  work  is  not 
always  immediately  observed.     The  change  or  loss  of  color 
called  fading,  with  which  all  are  familiar,  is  due  to  light. 
We  know  that  the  exposure  of  a  photographic  film  to  the 
light  for  a  small  fraction  of  a  second,  makes  the  film  different 
in  some  way.     It  is  possible  to  produce  a  picture  from  it 
afterward  by  the  application  of  the  proper  solutions.     The 
energy  of  light  has  rearranged  molecules  on  the  film  and 
formed  new  compounds. 

The  important  work  of  starch  making  is  carried  on  in  the 
green  leaves  of  plants  only  in  sunlight.  The  light  energy 
used  in  that  process  is  later  transformed  into  heat  energy 
or  muscular  energy  in  the  animals  using  the  plants  as  food. 
Energy  is  never  lost  or  destroyed,  though  often  it  is  so 
changed  that  the  ordinary  observer  does  not  recognize  it. 

Light  which  falls  upon  a  body  from  any  source  may  be 
transmitted,  passed  through  the  body;  reflected,  turned 
away;  or  absorbed,  taken  in.  Absorption  of  light  raises 
the  temperature  of  the  absorbing  body;  that  is,  light  energy 
is  transformed  into  heat.  Sunlight  is  transmitted  through 


122     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

glass  without  warming  it;  but  if  sunlight  falls  on  an  opaque 
surface,  part  of  the  light  is  absorbed  and  changed  into  heat. 

133.  Reflection.  —  No  one  expects  to  see  around  a  corner 
any  more  than  through  a  wall.  The  reason  why  one  cannot 
do  this  is  because  light  travels  in  straight  lines.  This  is  true 
of  reflected  light  as  well  as  of  light  coming  directly  from  its 
source.  A  polished  surface  of  metal  or  glass  makes  the  best 
reflector  of  light,  but  all  surfaces  reflect  a  part  of  the  light 
which  falls  upon  them.  It  is  by  this  reflection  of  light  that 
we  see  bodies  that  are  not  themselves  luminous. 

Vision  is  partly  a  process  of  the  mind.  We  are  accustomed 
to  the  fact  that  objects  are  visible  by  means  of  light  passing 


FIG.  57.  —  A  MIRROR 

1.  Explain  how  a  person,  by  aid  of  a  mirror,  can  know  what  is  at  one 
side  or  back  of  him.  2.  Why  does  a  kitten  placed  before  a  mirror  try  to 
look  behind  it?  3.  Explain  the  use  made  of  a  mirror  in  the  front  of  a  motor 
vehicle. 

in  straight  lines  to  the  eye.  Therefore  we  mentally  follow 
the  lines  back  to  the  place  from  which  they  seemed  to  start. 
The  reflection  seen  in  the  mirror  seems  to  come  from 
an  object  at  the  mirror  or  behind  it,  because  the  light 
comes  to  us  from  that  direction.  A  mirror  is  usually  so 
placed  that  objects  behind  or  at  one  side  of  the  observer 
can  be  seen  while  he  is  looking  straight  ahead.  Careful 
arrangements  of  mirrors  may  reflect  images  of  images  of 
objects.  One  object  may  have  several  images  if  the  mir- 
rors are  placed  parallel,  or  at  an  angle  to  each  other.  Some 


LIGHT 


123 


apparently  mysterious  phenomena  which  are  produced  on 
the  theater  stage  are  caused  by  adjustment  of  mirrors. 

134.  Refraction.  —  Light  is  refracted  (that  is,  bent)  in 
passing  obliquely  from  one  medium  into  another,  as  from 
air  into  glass  or  water.     It  is  this  refraction  that  causes  an 
oar  held  partly  under  water  to  look  bent  at  the  place  where 
it   leaves  the  water.     Light  from  the  oar 

blade  is  bent — and  therefore  its  direction 
is  changed  —  when  it  passes  from  water 
into  air.  The  light  seems  to  come  from 
a  different  position. 

The  apparent  change  of 
position  of  an  object  caused 
by  refraction  can  be  shown 
by  an  experiment.  Put  a 
button  on  the  flat  bottom  of 
an  opaque  dish  and  place 
yourself  in  such  a  position 
that  the  top  of  the  dish  just 
conceals  the  button  from 
view.  Pour  water  into  the 
dish  without  moving  the 
button  or  yourself.  The 
button  seems  to  rise  into 

view    Over    the   edge    of    the     one  edge  of  the"  coin."   The 'direction 

cup.     This  is  because  light    of 

from  the  button  which  passed 

above  your    eye  when    the 

dish  contained  only  air,  has 

been   bent    away   from   the    direction  in  which  it  started 

and  has  entered  your  eye. 

135.  Refracting  Bodies.  —  Prisms  and  lenses  are  trans- 
parent bodies  which  refract  light.     A  prism  has  three  or 
more  flat  surfaces.     If  light  passes  obliquely  through  any 
one  of  the  surfaces  of  a  prism,  two  effects  may  be  produced 


FIG.    58.  —  REPEACTION    CAUSING 
APPARENT  CHANGE  OF  POSITION 

1.  Why  could  not  the  eye  receive 
light  from  the  coin  a  if  the  basin 
were  empty?  2.  Ab  and  ac  show  the 
direction  of  two  rays  of  light  from 


^f  clf  ng(:d  ^st  above  the  point 

a.  Why  does  light  seem  to  have  come 
from  e  ?  3.  Through  what  mediums 
does  light  pass  from  the  coin  to  the 
eye? 


124      FIRST  YEAR  COURSE   IN   GENERAL  SCIENCE 

The  light  may  be  bent  from  the  direction  in  which  it  enters; 
and  it  may  be  separated  into  the  rainbow  colors  of  which 
white  light  is  composed.  An  object  seen  through  a  prism 
held  horizontally  seems  to  be  above  or  below  its  real  place, 
and  the  image  is  fringed  with  a  band  of  colors. 

Raindrops  act  like  prisms  in  separating  sunlight  into  rain- 
bow colors,  and  the  colored  light  reflected  to  the  observer 
from  many  drops  at  once,  makes  a  rainbow.  The  rainbow 
is  always  seen  in  the  part  of  the  sky  opposite  the  sun. 


FIG.  59.  —  A  PRISM 

Glass  prisms  used  in  the  study  of  light  have  generally  three  faces.  1.  If 
a  beam  of  light  falls  perpendicularly  upon  one  face,  it  will  not  be  bent  on 
entering  the  prism;  why  will  it  be  bent  on  leaving  the  other  side?  2.  In 
Fig.  59  the  beam  enters  obliquely,  is  bent,  passes  out  obliquely,  and  is  bent 
again.  How  many  changes  of  medium  are  there?  3.  What  happens  to  the 
rays  composing  the  beam,  besides  change  of  direction?  (The  names  of  the 
colors  are  violet,  indigo,  blue,  green,  yellow,  orange,  red.) 

A  lens  is  a  transparent  body  having  two  curved  surfaces 
or  one  curved  and  one  plane.  If  a  surface  is  like  the  inside 
of  a  hollow  sphere  it  is  a  concave  surface;  if  like  the  outside, 
it  is  a  convex  surface.  When  the  surfaces  are  so  combined 
that  the  lens  is  thinner  at  the  middle  than  at  the  edges,  it 
is  a  concave  lens  ;  if  the  lens  is  thicker  at  the  middle  than  at 
the  edges,  it  is  a  convex  lens.  A  convex  lens  can  be  used  as  a 
magnifying  glass.  When  it  is  held  a  short  distance  from  the 
object  examined,  the  eye  of  the  observer  receives  light  from 


LIGHT 


125 


an  image  apparently  larger  than  the  object.  Combinations 
of  lenses  are  used  in  telescopes,  opera  glasses,  and  compound 
microscopes. 

136.  The  Eye  and  the  Camera.  —  The  photographic 
camera  is  constructed  upon  the  same  principle  as  the  eye. 
Light  is  admitted  to  the  camera  through  a  small  opening; 
it  enters  the  eye  through  a  similar  opening  called  the  pupil. 
In  both  the  camera  and  the  eye,  the  light  then  passes  through 
a  convex  lens  into  a  dark  space  and  there  the  light  produces 
an  image.  In  the  camera,  the  image  is  formed  upon  a  plate 
or  a  film  coated  with  a  sensitive  substance  upon  which  light 
energy  causes  a  chemical  change.  In  the  eye,  the  image  is 


FIG.  60.  —  A  MAGNIFYING  GLASS 

1.  Follow  three  parallel  rays  of  light  o,  c,  b,  from-the  small  arrow  through 
the  lens;  how  is  their  relation  changed  after  leaving  the  lens?  2.  They 
pass  into  the  eye  and  fall  upon  the  retina;  where  do  they  seem  to  come 
from?  3.  What  is  the  difference  in  appearance  between  the  object  and  the 
image? 

formed  upon  the  retina,  which  is  a  membrane  upon  which 
the  ends  of  the  fibers  of  the  nerve  of  sight  are  spread  out. 

By  means  of  further  chemical  change  which  takes  place 
outside  of  the  camera,  the  image  on  the  film  is  developed  and 
is  made  permanent.  From  the  eye,  the  nerve  of  sight  trans- 
mits to  the  brain  the  effect  of  the  light  energy  and  we  are 
conscious  of  an  image;  we  "see"  the  object. 


126       FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

137.  Eye  Glasses.  —  Defects  of  vision,  such  as  near- 
sightedness,  farsightedness,  or  unlike  vision  of  the  two  eyes, 
can  generally  be  remedied  by  the  use  of  spectacles  or  eye 


FIG.  61.  —  A  CAMERA 

o  is  a  candle  from  which  two  rays  of  light  are  represented,  a  is  the 
opening  in  front  of  the  lens  of  a  camera,  p  is  a  plate  or  film,  i  is  the  image 
upon  the  plate.  Why  is  the  image  inverted? 


PUPIL- - 


FIG.  62.  —  THE  EYE 

In  Fig.  62  the  pupil  is  the  opening  through  which  light  enters  the 
eye;  the  lens  bends  the  rays  of  light  and  brings  them  together  near  the  retina, 
where  the  image  is  made.  The  muscles  change  the  shape  of  the  lens  as  the 
distance  of  objects  varies:  other  muscles  make  the  pupil  larger  or  smaller 
according  to  the  brightness  of  light.  1.  Comparing  Fig.  62  with  the  camera 
(Fig.  61),  tell  why  the  image  formed  upon  the  retina  is  inverted?  2.  Why 
does  it  not  seem  so  to  us? 

glasses,  which  are  often  lenses,  sometimes  convex  and  some- 
times concave.  These,  in  combination  with  the  lens  of  the 
eye,  bring  the  image  in  the  right  position  with  regard  to 
the  retina.  Without  these  external  lenses,  eye  strain  may 
be  caused  by  the  effort  of  the  muscles  to  change  the  shape 
of  the  lens  constantly.  These  muscles  in  the  eye  are 
adapted  only  for  occasional  use,  as  when  we  look  from  a 


LIGHT  127 

distant  object  to  one  near  at  hand.  They  readjust  the 
lens  of  the  eye  according  to  the  distance  of  the  objects 
viewed. 

One  should  consult  a  trained  oculist  before  wearing  glasses. 
There  is  great  danger  of  serious  injury  to  the  sight  in  using 
glasses  which  are  not  suited  to  the  eye.  Glasses  which  one 
person  has  found  in  every  way  beneficial  may  be  quite  the 
reverse  for  another.  Traveling  peddlers  of  eye  glasses 
should  not  be  patronized  any  more  than  street  venders  of 
medicines  which  "cure  everything." 

EXERCISES 

1.  What  heavenly  bodies  are  sources  of  light? 

2.  What  heavenly  bodies  shine  by  reflected  light? 

3.  Is  the  earth  a  source  of  light? 

4.  Light  travels  through  space  with  a  velocity  of  186,000  miles  per 
second.     How  many  times  would  it  pass  around  the  earth  in  one  second? 

6.  Why,  considering  the  statement  in  Ex.  4,  do  we  use  "  instantane- 
ous" in  speaking  of  the  passage  of  light  from  one  place  to  another  on 
the  earth? 

6.  Arrange  the  names  of  twelve  substances  in  tables  headed  trans- 
parent, translucent,  opaque. 

7.  What  weather  conditions  are  necessary  in  order  that  we  may  see 
a  rainbow? 

8.  What  is  your  position  with  relation  to  the  sun  when  you  see  a 
rainbow?     Why  must  it  be  so?  t 

9.  If  a  rainbow  is  visible  at  5  p.  m.,  in  what  part  of  the  sky  must 
it  be?     Why? 

10.  What  important  differences  are  there  in  the  operation  of  the 
camera  and  the  eye? 


CHAPTER  X  . 
ELECTRICITY  AND   MAGNETISM 

138.  Frictional  Electricity.  —  Twenty -five  hundred  years 
ago  a  Greek  discovered  by  experiment  that  if  a  piece  of 
amber  is  rubbed  with  wool  or  fur,  it  will  attract  very  light 
bodies,  such  as  bits  of  dry  paper,  lint,  or  pith.     These  light 
bodies  cling  to  the  surface  of  the  amber  for  a  time  and  then 
fly  off  as  if  repelled  by  it.     Similar  effects  can  be  produced 
by  rubbing  a  piece  of  sealing  wax  or  hard  rubber  with  fur, 
or  by  rubbing  glass  with  silk.     The  rubber,  glass,  or  similar 
body  is  said  to  be  charged  with  electricity  by  the  friction. 
The  bits  of  paper  or  pith  by  contact  become  charged  with 
the  same  form  of  electricity  as  the  rubber  or  the  glass,  and 
they  are  then  repelled. 

139.  Positive    and   Negative    Charges.  —  The  electricity 
upon  the  surface  of  glass  is  called  positive  electricity;  that 
upon  rubber  is  called  negative.     The  body  causing  the  fric- 
tion receives  an  opposite  charge  at  the  same  time.     The 
silk,  causing  friction  on  the  glass,  received  a  negative  charge; 
and  the  fur,  rubbed  on  wax  or  rubber,  received  a  positive 
charge.     A  body  which  is  positively  charged  is  attracted 
by  one  negatively  charged  and  repelled  by  one  positively 
charged. 

A  ball  made  of  pith  suspended  at  the  end  of  a  silk  thread 
shows  very  well  the  behavior  of  a  charged  body.  If  an 
electrified  glass  rod  is  brought  to  the  ball,  the  ball  flies  to 
the  glass  and  clings  to  it  for  a  time.  But  the  ball  receives 
from  the  glass  a  positive  charge  of  electricity.  Then  it 
jumps  away,  and  instead  of  hanging  vertically,  seems  pushed 
,away  from  the  glass  by  an  invisible  agent.  A  second  ball, 

128 


ELECTRICITY    AND    MAGNETISM 


129 


treated  like  the  first  and  brought  near  it,  is  repelled  by  the 
first.  But  if  one  ball  is  charged  from  the  glass  and  one 
from  wax,  they  attract  instead  of  repel  each  other.  The 
silk  thread  prevents  the  electricity  from  passing  off,  so  that 
the  balls  remain  charged  for  a  long  time  if  the  air  is  dry. 

140.  Conductors   and   Insulators.  —  If,  after  an  object  is 
charged  with  electricity,  the  hand  is  drawn  over  its  surface, 
the  electricity   disappears.     It  has  been   conducted   away 
through  the  hand  and  the  body 

to  the  earth.  We  call  the 
human  body  a  conductor  of 
electricity.  Many  of  the  metals 
are  much  better  conductors. 
Moist  air  and  damp  wood  are 
also  conductors,  but  not  such 
good  ones  as  metals.  Hard 
rubber,  glass,  dry  wood,  dry  air, 
porcelain,  and  sealing  wax  are 
non-conductors  or  insulators. 

Frictional  electricity  is  also 
called  statical  electricity,  from 
a  Latin  word  which  means  "to 
stay."  This  electricity  remains 
for  a  long  time  upon  the  surface 
of  insulated  bodies. 

Machines  have  been  con- 
structed that  will  produce  very 
strong  charges  of  statical  elec- 
tricity. Some  electrical  machines  will  cause  a  spark  to  pass 
through  several  feet  of  air.  Statical  electricity  is  used  by 
physicians  in  electrical  treatment  of  diseases  and  in  X-ray 
work.  It  was  useful  in  the  study  which  led  to  the  develop- 
ments of  wireless  telegraphy. 

141.  Lightning     and     Thunder.  —  If  a  sufficiently  large 
charge  of  electricity  accumulates  upon  an  insulated  conductor 


FIG.  63.  —  An  ELECTRIFIED 
PITH  BALL 

1.  The  pith  ball  is  attached 
to  a  metal  frame  by  a  silk  thread; 
why  not  by  a  wire?  2.  The  glass 
rod  has  been  rubbed  with  silk; 
how  does  it  affect  the  ball?  3. 
How  does  the  position  of  the 
thread  show  that  electricity  acts 
like  a  force? 


130     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

in  an  electrical  machine,  it  finally  discharges  itself  —  that 
is,  it  passes  through  the  air  to  the  nearest  body.  When 
the  discharge  takes  place,  a  sound  is  heard,  varying  from 
a  slight  snap  to  a  loud  cracking 'sound.  If  a  sheet  of 
paper  is  held  between  the  conductors,  a  hole  like  a  needle 
prick  shows  where  the  electricity  tore  its  way  through  the 
paper. 

A   flash    of   lightning   is   a   great   electric   spark.     Elec- 
tricity,  having   accumulated   upon   cloud   particles,  passes 


FIG.  64.  —  AN  ELECTRICAL  MACHINE 

Electricity,  which  is  on  the  surface  of  revolving  glass  plates,  passes  by 
metallic  conductors  to  knobs  at  the  front  of  the  machine.  If  these  knobs 
are  near  together,  a  succession  of  sparks  crosses  the  space  between  them  so 
rapidly  as  to  seem  continuous.  If  they  are  several  inches  apart,  the  dis- 
charges are  less  frequent  and  more  violent.  They  are  like  flashes  of  light- 
ning in  miniature. 

from  cloud  to  cloud  or  from  clouds  to  the  earth.  As  it 
tears  its  way  through  the  air,  it  causes  a  noise  whose  echoes 
reverberate,  making  a  succession  of  crashes  or  rolling  sounds 
which  we  call  thunder.  The  flash  of  the  electric  discharge 


ELECTRICITY   AND    MAGNETISM 


131 


reaches  the  eye  instantly.  The  noise  it  makes  travels 
more  slowly.  The  velocity  of  sound  in  air  is  about  1,100 
feet  per  second.  If  one  second  elapses  between  the  flash 


FIG.  65.  —  JOSEPH  HENRY:  PHYSICIST.     1797-1878 

He  was  a  born  experimentalist:  one  who  knew  how  to  cross-examine 
Nature  as  an  astute  lawyer  would  cross-examine  a  witness  and  thus  bring 
out  her  inmost  secrets.  He  was  one  of  those  men  by  whom  it  seems  as  if 
Nature  loves  to  be  cross-examined. — SIMON  NEWCOMB  in  Leading  American 
Men  of  Science. 

and  the  report,  the  discharge  is  1,100  feet  away,  or  more  than 
one  fifth  of  a  mile.     (One  can  count  five  in  one  second.) 

142.  Current  or  Voltaic  Electricity.  —  About  the  begin- 
ning of  the  nineteenth  century,  it  was  learned  that  if  two 
different  metals,  such  as  copper  and  zinc,  are  placed  in  a 
weak  acid  and  connected  by  a  wire  fastened  securely  to  the 
metals,  a  current  of  electricity  will  pass  through  the  wire. 
Carbon,  and  a  metal  upon  which  the  solution  acts  chemically, 


132      FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 


may  be  used  instead  of  two  metals.  There  must  be  chem- 
ical action  between  the  liquid  and  one  metal,  or  there  will  be 
no  current.  Such  a  combination  is  called  a  cell,  and  two  or 
more  cells  make  a  battery.  Electricity,  produced  in  this  way 
is  called  current  electricity  or  Voltaic  electricity,  from  Volta, 
one  of  its  discoverers.  (LABORATORY  MANUAL,  Exercise 
XIV.) 

The  two  pieces  of  metal,  the  liquid  between  them,  and  the 
wire  connecting  them  make  a  circuit,  or  path  for  the  current 
of  electricity.  The  ends  of  the  metals  where  the  conducting 
wire  is  attached  are  the  electrodes.  If  this  circuit  is  broken 


Simple  Cell  Battery 

FIG.  66.  —  A  SIMPLE  CELL  AND  A  BATTERY  OF  THREE  CELLS 

The  wider  piece  of  metal  represents  zinc,  the  other  copper.  Weak 
acid  acts  more  strongly  upon  zinc  than  upon  copper.  The  current  starts 
with  the  zinc,  is  conducted  by  the  acid  to  the  copper,  and  thence  by  wire 
back  to  the  zinc.  1.  How  many  substances  are  there  in  the  circuit?  2. 
What  change  would  be  produced  if  the  wire  were  broken? 

This  battery  contains  two  different  liquids  as  well  as  two  metals.  The  zinc 
in  weak  acid  is  in  a  porous  cup,  which  stands  in  a  jar  of  blue  vitriol  solution. 
The  current  passes  in  the  same  direction  as  in  a  simple  cell,  but  its  quantity 
and  intensity  vary  with  the  number  of  cells  and  the  connection  of  the  plates. 

by  separating  the  conductors  at  an  electrode,  or  by  taking 
one  metal  from  the  liquid,  no  current  passes. 

At  the  instant  of  breaking  the  circuit,  and  of  connecting  it 
again,  a  little  spark  at  the  electrodes  shows  the  presence  of 
electricity.  The  heat  of  this  spark  is  sufficient  to  light 
the  gas  at  a  burner  constructed  for  "  self-lighting."  An 


ELECTRICITY   AND    MAGNETISM 


133 


electric  spark,  also,  •  ignites  the  vapor  of  gasolene  in  the  gas 
engine  of  a  motor  boat  or  an  automobile. 

One  of  the  commonest  forms  of  cells  is  the  dry  cell,  which  is 
very  convenient  to  handle  because  it  contains  no  liquid 
which  might  be  spilled.  It  is  filled  with  a  paste  containing 
moist  substances  which  act  chemically  upon  one  of  the 
metals.  Liquid  cells,  when  used  up,  must  have  one  of  the 
electrodes  or  the  liquid  replaced  by  new  materials;  but 
the  dry  cell,  when  used  up,  must  be  replaced  by  an  entirely 
new  cell.  Dry  cells  are  much  used  in  operating  doorbells 
and  in  automobiles. 

Statical  electricity  accumulates  in  charges  on  various 
bodies,  and  as  soon  as  proper  connections  are  made,  it  dis- 
charges instantly.  Current 
electricity,  on  the  other  hand, 
has  a  continuous,  steady  flow. 
It  is  used  in  the  wires  of 
telephone  and  telegraph 
systems,  whereas  a  charge 

of  statical  electricity  is  useless 

.     .      FIG.  67.  —  A  MAGNETIC  COMPASS 
for  such  service,  because  it  is 

gone  in   an  instant. 

143.  Effects  of  an  Electric 
Current.  —  Some  of  the  effects 
of  current  electricity  are 
similar  to  those  of  statical 
electricity,  but  since  its 
quantity  and  intensity  can  be  better  regulated,  current 
electricity  is  of  much  greater  use.  The  effects  of  electricity 
are  heat,  light,  and  magnetization,  all  of  which  can  be 
produced  with  a  battery  of  a  few  cells.  Electricity  from  a 
battery  is,  however,  seldom  used  to  produce  any  of  these 
effects  for  practical  purposes.  Such  effects  are  produced  by 
a  method  which  is  described  later. 

A  simple  way  to  determine  whether  a  current  is  passing 


1.  The  box  surrounding  the 
magnetic  needle  is  usually  made  of 
brass;  why  not  of  iron?  2.  Should 
the  box  rest  in  a  vertical  or  horizontal 
position  when  used  to  determine 
direction?  Why?  3.  Why  are  pipes 
in  a  magnetic  laboratory  made  of 
brass  or  copper? 


134     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


through  a  wire  is  to  wind  the  wire  from  north  to 
south  around  a  magnetic  compass.  If  no  current  is  pass- 
ing, the  needle  will  keep  its  north  and  south  position  just 
as  if  no  wire  were  present;  but  if  a  current  passes  through 
the  wire,  it  causes  the  needle  to  turn  from  its  north-south 
position  toward  the  east  or  west,  according  to  the  direction 
of  the  current  above  the  needle. 

144.  Magnetism.  —  The  power  to  attract  pieces  of  iron 
or  steel  (which  is  a  form  of  iron)  is  called  magnetism.  Bodies 
having  this  property  are  magnets.  Iron  and  steel  are  more 
strongly  magnetic  than  any  other  metals.  If  a  light  piece  of 
iron  is  placed  near  a  magnet,  it 
moves  to  the  magnet  and  clings  to 
it;  but  if  the  magnet  is  the  lighter 
of  the  two  bodies,  it  moves  toward 
the  piece  of  iron. 

Not  all  pieces  of  iron  are  magnets, 
but  the  property  of  magnetism  may 
MAGNETIC  always  be  given  to  iron.  This  may 
be  done  by  striking  an  iron  bar  while 
it  is  held  in  a  north-south  position,  or 
by  rubbing  the  iron  with  a  magnet. 
In  either  of  these  cases,  a  bar  of  iron 
becomes  a  temporary  magnet,  but  a 

of  iron  to  the  east  of  either    steel  bar  retains  its  magnetism  and 
becomes  a  permanent  magnet. 

There  is  an  ore  of  iron  called 
magnetite  that  is  naturally  magnetic;  it  does  not  have 
to  be  magnetized.  It  is  found  in  veins  in  rocks. 

The  needle  in  a  compass  is  a  slender  piece  of  magnetized 
steel  which,  if  balanced  on  a  pivot,  will  swing  from  any  other 
position  until  it  lies  in  a  north  and  south  direction.  It  is 
upon  such  an  instrument  that  the  pilot  of  a  ship  or  a  surveyor 
depends  to  determine  the  points  of  the  compass  when  the 
sun  or  stars  are  hidden. 


FIG.  68.  — A 

NEEDLE 


The  needle  is  free  to 
move  around  a  pivot  upon 
which  it  is  supported.  1.  It 
is  at  rest,  pointing  north 


end?     2.     Would  a  copper 
rod  produce  the  same  effect? 


ELECTRICITY   AND    MAGNETISM 


135 


145.  Electricity  and  Magnetism.  —  The  construction  of 
telegraph  and  telephone  instruments  depends  on  the  fact 
that  an  electric  current  can  produce  magnetism  and  that 
magnetism  can  produce  an  electric  current.  When  an  elec- 
tric current  is  passed  around  a  bar  of  iron,  the  bar  becomes 
a  magnet,  but  it  re- 
mains one  only  as  long 
as  the  current  is  passing. 
A  temporary  magnet  is 
the  important  part  of  a 
telegraph  instrument. 

If  a  current  passes 
around  a  bar  of  steel, 
the  steel  becomes  a 
magnet,  and  does  not 
lose  its  magnetism  after 
the  current  ceases.  A 
permanent  magnet  is  a 
part  of  every  Bell  tele- 
phone receiver. 

If  a  magnet  is  put 
into  a  coil  of  wire,  a 
momentary  current  of 
electricity  passes 


FIG.  69.  —  THE  ELECTRIC  BELL 


In  the  figure,  m  is  an  electro-magnet, 
consisting  of  pieces  of  iron  around  which 
insulated  wire  is  wound.    When  b  is  pressed, 
through  the  wire.  When     a  current  can  pass  from  the  battery  through 
,    •  i      the  coils  of  wire  and  back  to  the  battery. 

the  magnet  IS  removed,     L  Whatisthe  effect  on  the  pieces  of  iron? 
a  Current    Starts   in  the     2.  At  a  there  is  another  piece  of  iron  on  a 
•  ,        -,  •  spring   connected  with  the  hammer  of  the 

Opposite  direction.     beU      What  is  the  effect  of  m  upon  a  when 
These    facts    are    made     the  button  is   pressed?     3.  Why  does  not 
£    •  j  this  effect  continue  when    pressure   is   re- 

use  of  in  producing    moved  from  6f 

electricity  by  machines 

called  dynamos.     They  furnish  powerful  electric  currents 

for  electric  lights,  electric  furnaces,  and  for  motors  which 

are  used  in  running  trolley  cars,  elevators,  and  all  kinds  of 

machines  in  factories. 


136      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


Electric  lights  are  of  two  kinds,  incandescent  and  arc 
lights.  In  the  incandescent  light  a  thread-like  conductor, 
called  the  filament,  is  heated  white-hot  by  its  resistance  to 
the  electric  current  passing  through,  it.  This  filament  is 
enclosed  in  a  bulb,  which  is  either  a  partial  vacuum  or  is 
filled  with  nitrogen.  The  filament  would  be  burned  if  the 
bulb  contained  air.  Arc  lights  are  caused  by  a  powerful 
electric  current  passing  between  two  carbon  rods  slightly 

separated  from  each  other. 
This  separation  causes  a  re- 
sistance which  heats  the  ends 
of  the  carbons  white-hot. 
These  white-hot  carbon  ends 
give  the  brilliant  light.  The 
hot  carbon  vapor,  which  fills 
the  space  between  the  ends, 
conducts  the  current. 

146.  Transformation  of 
Energy.  —  Whenever  an 
electric  motor  is  used,  it 
must  be  run  by  power 
furnished  by  a  dynamo, 
which  in  turn  is  run  by  water 


FIG.  70.  —  AN  ELECTRIC  GENER- 
ATOR OR  DYNAMO 

Such    a   machine    as   this   is    a 


dynamo.    It  consists  of  a  revolving     power   Or  by  steam.       In  the 

former    case,     the    force    of 

magnets  set  up  currents  of  electricity,     gravity   gives   energy    to    the 


core    of    electro-magnets    within    a 
great    permanent    magnet.     The 


first  in  one  direction  and  then  in  the    foil™  watpr-    in    the  rase  of 
opposite  direction,   so  rapidly   that.   * 
they  seem  continuous.    The  currents 
pass  off  by  wires  connected   at  the 
axle.     The  revolution  of  the  core  is 


steam, 
duced 


the    energy    is    pro- 
>y  the  chemical  action 


caused  by  power  transmitted  by    a     between  fuel  and  the  Oxygen 


belt  over  the  axle  at  the  side.    What 
power  might  be  used? 


of  the  air. 

There  are  several  steps  in 
the  transformation  of  chemical  energy  into  electrical  energy. 
Chemical  energy  from  oxidation  of  coal  becomes  heat  energy; 
heat  causes  the  expansion  of  steam  which  produces  energy 


ELECTRICITY    AND    MAGNETISM  137 

of  motion  in  a  piston;  this  motion,  transmitted  by  the  parts 
of  an  engine  to  a  dynamo,  produces  electrical  energy. 

The  waterfall  and  the  steam  boilers  may  be  many  miles 
away  from  the  motor  and  the  machines.  The  electricity 
can  be  conveniently  carried  by  wires,  properly  insulated, 
underground  or  overhead.  Current  is  thus  supplied  to 
towns  which  have  no  water  power  or  railroad  facilities  for 
bringing  coal  by  which  they  could  produce  electricity. 
Streets  and  houses  in  rural  districts  are  now  better  lighted 
than  were  those  of  a  large  city  fifty  years  ago.  Cars  run  by 
electricity  furnish  cheap  and  rapid  conveyance  which  brings 
the  city  and  the  country  nearer  together,  to  the  advantage 
of  both. 

EXERCISES 

1.  What  kind  of  electricity  is  developed  by  stroking  a  cat's  fur? 

2.  Explain  the  spark  that  passes  from  the  hand  to  the  cat's  body 
after  the  stroking. 

3.  Which  is  a  better  conductor,  dry  or  moist  air? 

4.  Why  does  a  body  retain  a  charge  better  on  a  dry  day? 

6.    How  far  away  is  an  electric  flash  if  one  can  count  twenty  between 
the  moment  of  seeing  the  flash  and  hearing  the  thunder? 

6.  Name  all  the  parts  of  the  circuit  of  a  simple  cell  whose  metal 
plates  are  connected  by  a  copper  wire. 

7.  Why  is  it  necessary  to  cover  telephone  and  electric  light  wires? 

8.  Why  are  glass  or  porcelain  coverings  used  where  telegraph  wires 
are  supported  on  poles? 

9.  What  is  meant  by  a  "  live  wire  "? 

10.  Name  changes  in  the  form  of  energy  between  a  waterfall  which 
is  used  in  producing  electricity  and  a  trolley  car  run  by  electricity. 


CHAPTER  XI 
HOW   MATTER   CHANGES 

147.  Physical     Changes.  —  A  small  bar  of  iron  rubbed 
upon  a  magnet  becomes  a  magnet  itself;  that  is,  it  acquires 
the  property  of  attracting  pieces  of  iron  or  steel.     Left  un- 
touched for  a  time,  it  loses  its  new  property;   but  the  iron 
was  iron  and  nothing  else  all  the  time.     Mercuric  iodide,  a 
red  powder,  on  being  heated  becomes  yellow.     When  cooled 
again,  it  returns  to  its  original  red  color;  it  is  the  same  sub- 
stance as  before.     If  a  piece  of  wood  is  changed  to  sawdust, 
or  a  piece  of  stone  crushed  to  powder,  the  wood  and  stone 
retain  their  former  characteristics  though  they  may  never 
again  become  a  single  body.     If  sugar  or  salt  is  dissolved  in 
water  and  the  solution  is  exposed  to  the  air,  the  water  evapo- 
rates and  the  sugar  or  salt  reappears  unchanged.     Such 
changes  as  these  are  physical  changes.     Condensation  and 
evaporation,  freezing  and  melting,  expanding  and  contract- 
ing, are  all  physical  changes. 

A  physical  change  is  one  that  does  not  permanently 
change  the  properties  of  a  substance  nor  produce  any  change 
in  its  composition. 

148.  Chemical   Changes.  —  A  lump  of  sugar  placed  on  a 
hot  stove  melts.     A  cloud  of  white  smoke  rises  from  it  and 
after  a  time  a  crisp,  black  solid  is  all  of  the  sugar  that 
remains  on  the  stove.     This  residue  looks  like  charcoal;   it 
does  not  dissolve  in  water;   it  has  no  sweet  taste.     It  has 
permanently  lost  its  characteristic  properties  of  whiteness, 
solubility,  and  sweetness.     It  is  not  sugar. 

A  chemical  change  is  one  that  causes  a  loss  of  characteris- 
tic properties  because  of  a  change  in  the  composition  of  the 
substance. 

138 


HOW  MATTER  CHANGES  139 

If  mercuric  oxide,  a  red  powder,  is  heated  slowly  in  a  tube 
to  a  high  temperature,  it  does  not  behave  like  the  red  powder 
described  in  §147.  If  a  stick  with  a  spark  on  the  end  is  held 
in  the  tube  while  the  mercuric  oxide  is  being  heated,  the 
spark  bursts  suddenly  into  flame.  This  shows  that  there  is 
now  something  besides  air  in  the  tube.  When  the  tube  is 
allowed  to  cool,  a  gray  shining  substance  appears  on  the  in- 
side. This  does  not  return  to  the  form  of  a  red  powder,  no 
matter  how  long  it  stands.  The  mercuric  oxide  was  a  com- 
pound that,  on  being  heated,  gave  off  a  gas  and  mercury. 
The  gas  made  the  wood  blaze,  and  the  mercury  remained 
in  tiny  globules  on  the  inside  of  the  tube.  This  change 
was  a  chemical  change  called  decomposition.  In  decom- 
position, a  compound  separates  into  two  or  more  different 
substances. 

If  the  end  of  a  thin  piece  of  magnesium  is  heated  in  a 
flame,  it  burns.  When  it  is  cooled,  the  substance  remaining 
is  quite  different  from  the  original  magnesium  in  color,  tex- 
ture, and  composition.  There  has  been  a  chemical  change. 
Oxygen  from  the  air  has  united  with  the  magnesium,  making 
a  new  substance,  magnesium  oxide.  When  two  or  more 
substances  unite  to  form  new  substances,  there  is  a  chemical 
change  called  combination. 

Decomposition  and  combination  include  all  kinds  of  chemi- 
cal changes.  Burning,  decay,  separation  of  metals  from  ores, 
and  digestion  of  food  are  chemical  changes,  and  all  involve 
either  decomposition  or  combination,  or  both. 

149.  Oxidation.  —  The  most  abundant  element  in  the 
earth  is  oxygen.  It  is  a  gas  which  exists  as  an  element  mixed 
with  other  gases  in  air.  The  union  of  any  other  element 
with  oxygen  is  called  oxidation,  and  the  new  substance  or 
product  is  always  an  oxide.  Oxidation  is  the  most  common 
chemical  change. 

When  a  substance  burns,  it  is  because  one  or  more  of  its 
elements  combines  with  the  oxygen  of  the  air.  If  the  combi- 


140     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

nation  takes  place  rapidly,  noticeable  quantities  of  heat  and 
light  are  given  off,  and  the  process  is  called  combustion  or 
burning.  If  the  change  takes  place  slowly  without  any 
flame,  the  process  is  called  simply  oxidation  or  slow  combus- 
tion. The  compounds  formed  in  both  cases  are  oxides. 

The  burning  and  the  decay  of  wood  are  both  oxidation 
and  form  the  same  compounds.  In  the  case  of  burning, 
the  heat  is  intense  for  a  short  time.  In  decay,  the  change 
in  temperature  is  too  slight  to  be  detected  by  ordinary  ob- 
servation, and  the  process  may  take  many  years. 

150.  Spontaneous    Combustion.  —  The  slow  oxidation  of 
oily  rags  or  paper  is  often  the  cause  of  accidental  fires.     The 
oil  slowly  unites  with  the  oxygen  of  the  air  and  heat  is  pro- 
duced.    If  the  rags  are  loosely  placed,  the  heat  may  be  given 
off  as  fast  as  it  is  made  and  no  harm  is  done.     If  the  matter 
is  packed  closely  or  is  in  a  small  space  like  a  closet  where 
there  is  little  change  of  air,  the  temperature  rises  until  it  is 
high  enough  to  set  the  combustibles  on  fire.     This  is  called 
spontaneous  combustion. 

151.  Explosions.  —  A   little   gunpowder   spread   upon   a 
stone  and  set  on  fire  burns  quickly  but  quietly,  making  a 
large  amount  of  smoke.     A  smaller  quantity  of  gunpowder 
in  a  firecracker  burns  quickly  and  bursts  the  firecracker, 
making  a  loud  noise.     In  both  cases  the  powder  burns;    in 
the  second  case  it  results  in  an  "  explosion."     The  noise  pro- 
duced in  this  way  and  the  bursting  are  both  called  explosions. 
In  both  cases  of  burning,  a  large  amount  of  gas  is  formed 
quickly;   in  the  second  case  the  gas  is  confined  and  makes 
room  for  itself  by  pushing  away  the  confining  walls. 

Explosives  are  made  for  the  purpose  of  pushing  the  pro- 
jectile from  a  gun,  the  rocket  from  its  fastening,  the  rock 
from  the  side  of  a  mountain.  An  explosive  always  contains 
two  things:  (1)  a  substance  which,  on  being  struck  or 
heated,  sets  free  oxygen  to  insure  rapid  combustion;  and 
(2)  a  combustible  material  which,  when  united  with  oxygen, 


HOW  MATTER  CHANGES  141 

makes  a  large  volume  of  gas.  The  rapid  expansion  of  this 
gas  produces  the  desired  explosion.  Gunpowder,  the  ex- 
plosive longest  in  use,  contains  saltpeter  to  furnish  oxygen, 
and  charcoal  and  sulphur  for  combustibles. 

152.  The  Relation  of  Oxidation  to  Life.  —  The  unfold- 
ing of  a  flower  bud,  the  turning  of  a  leaf  toward  the  sun,  the 
lifting  of  the  foot  or  the  hand,  the  beating  of  the  heart,  are  all 
forms  of  work  and  therefore  require  energy.     Energy  in 
living  things  is  the  result  of  oxidation,  and  all  living  things 
use  oxygen  to  produce  energy.     Part  of  the  energy  shows 
itself  as  heat  or  increase  in  body  temperature  —  a  temper- 
ature which  is  higher  in  many  animals  than  in  plants. 

Life  ceases  when  no  energy  is  produced.  That  is  why 
suffocation,  or  lack  of  air,  produces  death.  Drowning  is  a 
form  of  suffocation.  The  loss  of  life  in  a  burning  building  is 
not  always  the  result  of  burning  to  death;  it  is  often  due  to 
suffocation.  Irritating,  suffocating  gases  are  made  by  the 
burning  of  wood,  as  we  all  know  if  we  have  ever  sat  near  a 
smoking  fireplace.  Such  gases  in  a  burning  building  may 
fill  rooms  and  stairways  not  touched  by  fire.  One  of  the 
first  effects  of  suffocation  is  unconsciousness.  If  the  victim 
is  rescued  and  supplied  with  fresh  air,  fatal  results  may  be 
prevented. 

When  injurious  gases,  as  coal  gas  or  illuminating  gas,  are 
mixed  with  air,  the  result  is  not  simply  suffocation  but  a 
poisoning.  This  is  called  asphyxiation. 

153.  The  Ignition  Point.  —  The  temperature  which  a  sub- 
stance must  have  before  it  takes  fire,  or  ignites,  is  called  the 
kindling  point  or  ignition  point.     The  kindling  point  of  gaso- 
lene vapor  is  so  low  that  it  is  not  safe  to  use  gasolene  in  a 
room  where  there  is  a  fire  or  flame  of  any  kind.     Alcohol 
also  has  a  very  low  ignition  point.     Hot  alcohol  is  some- 
times recommended  for  treatment  of  bruises,  but  the  alcohol 
cannot  safely  be  placed  in  a  dish  on  the  stove;    it  may, 
however,  be  heated  over  a  dish  of  hot  water. 


142     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


154.  The  Law  of  Conservation  of  Matter.  —  A  body 
may  be  destroyed  by  burning,  or  may  disappear  by  evapo- 
rating, but  the  matter  of  which  it  was  composed  still  exists 
-  perhaps  in  some  different  state  or  united  with  other  mat- 
ter to  form  a  new  substance.  This  is  known  as  the  Law  of 
Conservation  of  Matter.  The  law,  briefly  stated,  is  this: 
the  quantity  of  matter  in  the  universe  is 
constant;  or  in  other  words,  matter  is 
indestructible. 

When  an  element  is  completely 
burned,  or  oxidized,  the  product  (that 
is,  the  new  substance  formed)  weighs 
more  than  the  original.  To  the  weight 
of  the  element  that  was  burned  is  added 
the  weight  of  the  oxygen.  Twelve 
grams  of  carbon  completely  burned  give 
forty-four  grams  of  carbon  dioxide. 

If  a  solid,  in  burning,  forms  chiefly 
gases,  the  residue  (that  is,   the  solid 
remaining    after    combustion    ceases) 
through ThiiT~siit  and  is    weighs  less  than  the  original,  because  a 
pushed  up  to  the  top,          t  of   the  matter  has  passed  off  as 

where  it    is   lighted. 


FIG.  71. — BUNSEN 
BURNER 

Inside,  at  the  bottom 
of  the  upright  tube,  is  a 
small  tube  with  a  narrow 
slit.  The  gas  comes 


gaseous  oxides.  Wood  is  a  fuel  which 
illustrates  this  fact.  The  ashes  weigh 
less  than  the  original  wood. 

155.  The  Law  of  Definite  Pro- 
portions. —  Any  given  compound  is 
always  made  up  of  the  same  elements  in 
the  same  definite  proportions  by  weight. 
In  combustion  12  grams  of  carbon  will 
unite  with  32  grams  of  oxygen,  or  6 
grams  of  carbon  with  16  grams  of  oxygen,  and  there  will  be 
no  remainder  of  carbon  or  oxygen.  But  if  there  are  13  grams 
of  carbon  and  only  32  grams  of  oxygen,  one  gram  of  carbon 
will  remain  uncombined.  The  same  law  holds  true  for 


When  the  holes  at  the 
base  of  the  upright  tube 
are  open,  air  enters  and 
mixes  with  the  gas  before 
it  reaches  the  top.  1. 
How  does  that  affect 
combustion?  2.  If  the 
holes  are  open,  the 
flame  is  pale  blue;  if 
closed,  it  is  luminous. 
Which  is  like  the  flame 
of  a  gas  stove? 


HOW  MATTER  CHANGES 


143 


other  combinations.  This  is  called  the  Law  of  Definite 
Proportions. 

If  the  proper  weights  of  the  given  substances  are  well 
mixed,  so  that  each  small  particle  is  near  those  with  which 
it  will  unite,  chemical  combination  takes  place  more  rapidly. 
Gases  mix  most  readily,  and  liquids  next;  finely  powdered 
solids  mix  less  readily  than  gases  and  liquids,  but  better 
than  large  masses  of  solids. 

The  burners  of  gas  stoves  and  Bunsen  burners,  such  as  are 
used  in  laboratories,  are  provided  with  holes  for  the  admission 


FIG.  72.  —  THE  FIRE  Box  OF  A  FURNACE 

1.  Why  is  a  grate,  and  not  a  sheet  of  metal,  provided  for  the  coal 
to  rest  upon?  2.  At  which  door  does  air  enter  for  the  process  of  oxidation? 
3.  What  is  such  an  opening  called?  4.  How  does  the  amount  of  air  affect 
combustion?  5.  Explain  the  effect  upon  the  fire  when  the  other  door  is 
left  open. 

of  air  near  the  place  where  the  gas  enters.  Thus  air  and 
illuminating  gas  are  mixed  and  come  to  the  opening  to- 
gether, and  when  a  flame  is  applied,  every  particle  of  illu- 
minating gas  is  in  contact  with  the  oxygen  of  the  air  and 
burns  rapidly.  Each  particle  of  gas,  however,  will  unite 
with  only  a  certain  amount  of  oxygen,  no  matter  how 
much  is  furnished.  (LABORATORY  MANUAL,  Exercises  XV, 
XVI.) 


144      FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 


Stoves  and  furnaces  have  an  opening  below  the  firebox. 
Air  entering  there  mixes  with  the  hot  fuel  and  helps  to  pro- 
duce rapid  combustion.  If  the  opening  is  closed,  the  current 
of  air  does  not  pass  through  the  fuel,  combustion  is  less  rapid, 
and  the  fire  is  "checked." 

156.  Extinguishing  Fires.  —  Two  conditions  are  necessary 
to  produce  a  fire:  a  temperature  at  or  above  the  ignition 
point,  and  the  presence  of  oxygen.  There  are  consequently 


TST 


J_^_  _     LOOSE 

STOPPER 


SODIUM 

CARBONATE 


FIG.  73.  —  A  CHEMICAL  FIRE  EXTINGUISHER 

When  the  cylinder  is  turned  "upside  down,"  according  to  directions, 
acid  runs  out  of  a  loosely  stoppered  bottle  inside,  into  a  strong  solution  of 
sodium  carbonate  or  sal  soda.  This  causes  a  large  quantity  of  carbon  dioxide 
to  be  made  in  a  small  space.  Under  its  own  pressure,  the  gas  is  pushed 
out  of  the  small  hose  attached,  bringing  some  liquid  with  it. 

two  methods  of  extinguishing  fires:  first,  by  cooling  the 
burning  material  below  its  ignition  point;  and  second,  by 
preventing  air  from  coming  in  contact  with  the  burning  ma- 
terial. In  the  first  method  water  is  used.  The  second 
method  may  be  successful  when  the  fire  is  confined  to  a  small 
area;  for  instance,  blankets  or  a  suffocating  gas  may  be 


HOW  MATTER  CHANGES  145 

used  to  cover  the  flames  and  keep  out  the  air.  If  the  clothing 
of  a  person  takes  fire,  the  quickest  and  safest  method  of  ex- 
tinguishing the  flame  is  to  wrap  the  body  closely  in  a  woolen 
rug  or  blanket.  This  excludes  the  air.  If  the  accident 
occurs  out  of  doors,  the  victim  may  be  rolled  in  soft  earth 
or  covered  with  earth. 

157.  Chemical  Engines.  —  Chemical  engines  and  hand 
extinguishers  furnish  a  spray  of  water  and  carbon  dioxide, 
a  gas  in  which  combustion  will  not  take  place.  Carbon  di- 
oxide is  a  heavy  gas  and  spreads  over  the  fire  in  much  the 
same  way  that  a  wet  blanket  might,  thus  shutting  out  the 
air  and  preventing  combustion  until  the  combustible  sub- 
stance has  cooled.  It  would  take  a  great  quantity  of  water 
to  produce  the  same  effect,  and  much  injury  to  goods  would 
be  caused  by  the  water. 

If  kerosene  is  spilled  and  burning,  carbon  dioxide  is  a  better 
extinguisher  than  a  stream  of  water.  As  kerosene  is  lighter 
than  water,  the  water  would  go  under  the  burning  kerosene, 
leaving  it  still  exposed  to  the  oxygen  in  the  air.  Carbon 
dioxide,  however,  would  cover  the  kerosene  and  extinguish 
the  flames. 

EXERCISES 

1.  Arrange  the  following  occurrences  under  the  proper  heading,  as 
Physical  Change  or  Chemical  Change:  melting  of  glass,  burning  of  paper, 
magnetizing  of  iron,  boiling  of  water,  rusting  of  iron,  dissolving  of  salt, 
drying  of  clothes,  explosion  of  a  torpedo,  formation  of  ice,  tarnishing 
of  silver,  lighting  the  gas,  extinguishing  a  fire,  evaporation  of  water. 

2.  What  is  meant  by  the  statement  that  the  kindling  point  of  coal 
is  higher  than  that  of  wood? 

3.  Which  gives  a  higher  temperature,  slow  or  rapid  burning? 

4.  A  given  weight  of  carbon  unites  with  2f  times  its  own  weight  of 
oxygen,  in  case  of  complete  combustion,     (a)  How  much  oxygen  will 
15  g.  of  carbon  require?     (6)  What  weight  of  carbon  dioxide  is  made 
from  this  combination? 

5.  1,000  cu.  cm.  of  carbon  dioxide  weigh  2  g.     In  Ex.  4,  how  many 
thousand  cubic  centimeters  of  gas  would  be  made? 

6.  How  does  water  act  in  putting  out  a  fire? 


146     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

7.  Why  is  prompt  action  with  a  limited  amount  of  water  more  suc- 
cessful in  extinguishing  a  fire  than  a  larger  amount  of  water  after  the 
fire  is  well  started? 

8.  Why  does  not  the  carbon  dioxide  formed  by  combustion  extin- 
guish the  flames  which  produce  it? 

9.  If  some  kerosene  were  spilled  and  burning,  why  would  sand  be 
a  better  extinguisher  than  water? 

10.  Compare  suffocation  with  the  process  of  putting  out  a  fire. 

11.  Why  is  oxidation  the  commonest  change  in  matter?     Give  three 
illustrations  of  oxidation  not  mentioned  in  the  text. 


CHAPTER  XII 
THE    COMMON    ELEMENTS    OF   THE    EARTH 

158.  Oxygen.  —  Oxygen  is  the  most  abundant  as  well  as 
the  most  important  of  all  the  elements.  Without  it,  there 
could  be  no  life.  It  has  no  color,  odor,  or  taste.  It  does  not 
burn,  but  causes  other  substances  to  burn.  It  is  a  part  of 
the  air  we  breathe,  of  the  water  we  drink,  and  of  almost 
everything  we  use  for  food.  As  a  pure  element,  however, 
we  have  almost  no  practical  use  for  oxygen.  Physicians 


FIG.  74.  —  BURNING  IRON  WIRE  FIG.  75. — UXYHYDROGEN  LAMP 

FIG.  74. — The  end  of  a  piece  of  iron  wire  tipped  with  a  bit  of  burning 
sulphur  is  put  into  a  bottle  of  oxygen.  The  sulphur  burns  very  brightly 
and  heats  the  end  of  the  wire,  which  becomes  dazzlingly  bright  and  throws 
off  bright  sparks.  After  the  burning  ceases,  the  inside  of  the  jar  is  found 
covered  with  a  brown  powder.  1.  What  could  the  powder  be?  2.  Why 
does  the  burning  stop  before  the  iron  is  used  up? 

FIG.  75. — Acetylene,  another  combustible  gas,  is  sometimes  used  instead 
of  hydrogen  in  such  a  lamp.  The  gas  H  is  first  turned  on;  it  enters  the  tube 
6,  and  is  lighted  at  e.  1.  How  can  it  burn  before  the  oxygen  is  turned  on? 
2.  Oxygen  passes  through  the  tube  a  and  out  at  c.  Why  is  the  flame  hotter 
after  oxygen  is  turned  on? 

147 


148      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


furnish  it  pure   to  patients  to  breathe  in  some  cases   of 
extreme  weakness,  thus  prolonging  life  a  short  time. 

159.  Hydrogen.  —  There  are  two  other  gaseous  elements, 
hydrogen  and  nitrogen,  that  are  common  enough  to  be  of 
great  interest.  They  are  not  very  well  known  because  un- 
der ordinary  conditions  they  are,  like  oxygen,  invisible. 
Hydrogen,  the  lightest  substance  known,  is  only  about  one 
fourteenth  as  heavy  as  air.  It  is  not  often  found  in  nature 


FIG.  76. — BURNING  HYDROGEN 


FIG.  77. — ELECTROLYSIS  OF  WATER 


FIG.  76. — 1.  What  is  the  product  of  hydrogen  burning  openly  in  air? 
2.  Could  the  substance  be  seen?  3.  What  would  be  the  effect  of  placing 
a  cool  jar  over  the  flame?  Explain. 

FIG.  77. — The  two  arms  of  the  U-shaped  tube  were  full  of  water  when  the 
current  began  to  pass  between  the  pieces  of  platinum  near  the  bend.  1. 
Compare  the  condition  of  the  two  arms  now.  2.  What  is  the  meaning  of 


in  the  gaseous  form,  as  oxygen  is,  uncombined  with  other 
elements;  but  it  makes  one  ninth  of  the  weight  of  water 
and  is  found  in  many  other  compounds.  Hydrogen  is  com- 
bustible, that  is,  it  will  burn.  When  burned  in  pure  oxygen, 
it  makes  one  of  the  hottest  flames  known  —  the  oxyhydro- 
gen  flame,  which  is  used  to  melt  metals  and  minerals  that  do 
not  melt  in  ordinary  fires.  It  is  also  used  to  heat  white-hot 
the  block  of  lime  which  gives  the  intense  light  used  in  many 


COMMON  ELEMENTS  OF  THE  EARTH  149 

stereopticons.     The  lightness  of  hydrogen  makes  it  useful  in 
filling  balloons. 

160.  The  Composition  of  Water.  —  Whenever  hydrogen 
is  burned  in  oxygen  or  in  air,  it  unites  with  the  oxygen  and 
forms  a  vapor,  which  on  cooling  condenses  to  a  liquid.     This 
liquid  is  pure  water.     On  the  other  hand,  by  an  electric 
current  (Fig.  77)  water  may  be  decomposed  into  two  gases, 
which,  on  being  tested,  prove  to  be  oxygen  and  hydrogen. 
When  the  volumes  of  these  two  gases  are  measured,  it  is  found 
that  there  is  twice  as  much  hydrogen  as  oxygen.     Weighing 
the  gases  shows  that  the  oxygen  weighs  eight  times  as  much 
as  the  hydrogen.    Thus  it  is  shown  that  water  is  composed  of 
two  volumes  of  hydrogen  to  one  of  oxygen,  or  one  unit  of 
weight  of  hydrogen  to  eight  of  oxygen.    From  these  measure- 
ments it  is  seen  that  when  equal  volumes  of  these  gases  are 
considered,  oxygen  weighs  sixteen  times  as  much  as  hydrogen. 

161.  Nitrogen.  —  The  gas  nitrogen  can  best  be  described 
by  negatives.     It  does  not  burn  as  hydrogen  does,  nor  aid 
in  burning  as  does  oxygen,  and  it  does  not  readily  unite  with 
other  substances  to  form  compounds.     But  there  are  many 
compounds    of    nitrogen    which   are  far  from   negative   in 
character.     Combined  with  hydrogen,  it  forms  the  pungent 
gas  ammonia.      With  hydrogen  and  oxygen,  it  makes  nitric 
acid,  which  dissolved  metals.     The  explosives  —  dynamite, 
nitroglycerine,    and    gunpowder  —  contain    compounds   of 
nitrogen. 

Compounds  of  nitrogen  are  necessary  in  the  food  of  ani- 
mals; these  compounds  are  obtained  from  plant  food  or 
from  the  bodies  of  animals  that  have  eaten  plant  food. 
Plants  obtain  a  large  amount  of  their  nitrogen  from  com- 
pounds of  nitrogen  in  the  soil. 

Air  is  a  mixture  of  nitrogen  and  oxygen  in  the  proportion 
of  about  four  volumes  of  nitrogen  to  one  of  oxygen,  to- 
gether with  a  very  small  proportion  of  carbon  dioxide, 
water  vapor,  and  some  other  gases. 


150     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

162.  Chlorine.  —  Chlorine  is  of  interest  principally  be- 
cause of  the  importance  of  some  of  its  compounds.     The  ele- 
ment is  a  greenish-yellow  gas  of  disagreeable  odor;    when 
breathed,  it  is  irritating  and  suffocating.     It  does  not  exist 
free  in  nature,  but  in  combination  with  other  elements  it  is 
found  in  many  minerals.     The  most  abundant  compound  of 
chlorine  is  common  salt,  which  is  found  both  in  the  ocean 
and  as  a  solid  mineral  in  the  earth.     Chlorine  can  be  pre- 
pared from  common  salt  for  use  in  bleaching  or  in  disin- 
fecting.    A  powder  called  chloride  of  lime  is  commonly  used 
for  these  purposes,  as  it  gives  off  its  chlorine  very  readily. 

163.  Carbon.  —  Most  of  the  solid  elements  are  metals, 
but  there  are  three  common  solid  elements  —  carbon,  sul- 
phur, and  phosphorus  —  which  are  not  metals. 

Carbon  is  black,  except  in  the  case  of  the  diamond,  which 
is  usually  colorless.  There  are  several  other  varieties  of  the 
element  carbon:  graphite  (called  black  lead),  lampblack  or 
soot,  coke,  and  charcoal.  Mineral  coal  is  an  impure  form 
of  carbon. 

All  forms  of  carbon  are  combustible,  but  they  must  have 
a  comparatively  high  temperature  in  order  to  burn.  The 
kindling  point  of  charcoal  is  lowest,  and  that  of  graphite  is 
highest.  When  charcoal  and  diamond  are  burned  in  pure 
oxygen,  they  both  form  the  same  product,  carbon  dioxide. 
This  proves  that,  unlike  as  they  are  in  appearance  and 
properties,  charcoal  and  diamond  are  the  same  element. 

164.  Coal    and    Charcoal.  —  Many,  many  thousands  of 
years  ago  areas  of  land  overgrown  with  great  forests  slowly 
sank  and  were  covered  with  water.     The  fallen  trees  were 
buried  under  layers  of  sand  and  mud  which  settled  in  the 
water.    The  plant  material,  shut  away  from  the  air,  oxidized 
very  slowly.     In  the  process  of  slow  combustion,  gases  were 
formed  and  passed  away,   leaving  beds  of  solid   matter, 
mostly  carbon,  which  is  called  coal.     Coal  is  the  residue  of 
incomplete  combustion  of  wood  and  other  vegetable  matter. 


COMMON   ELEMENTS  OF   THE  EARTH  151 

Some  of  the  beds  beneath  the  coal  contained  remains  of 
marine  life.  Decay  caused  gases  rich  in  carbon  to  be  forced 
into  the  crevices  of  the  rocks,  where  some  of  these  gases 
\\ere  condensed  into  liquid  petroleum.  When  borings  are 
made  through  the  rocks  near  certain  coal  regions,  petroleum 
or  a  gas  comes  from  the  openings,  sometimes  for  years  with- 
out cessation.  The  products  from  distillation  of  petroleum 
are  very  numerous.  Among  those  most  widely  used  are 
kerosene,  gasolene,  vaseline,  and  paraffin.  Natural  gas  is 
used  for  fuel  as  well  as  for  light  in  many  parts  of  the  United 
States. 

Charcoal  is  prepared  by  heating  wood  in  a  kiln  or  oven, 
where  air  cannot  enter.  Gases  and  steam  are  driven  off, 
and  carbon  in  a  solid,  nearly  pure  form  is  left.  The  process 
is  similar  to  the  method  by  which  coal  was  made  under 
the  rocks  during  many  centuries,  but  is  very  much  more 
rapid. 

Carbon  occurs  in  many  compounds  in  the  bodies  of  plants 
and  animals.  It  is  the  union  of  this  carbon  with  oxygen 
(slow  combustion)  which  furnishes  the  energy  needed  to  keep 
the  body  alive.  All  kinds  of  grains  and  fats  furnish  carbon 
compounds  in  large  quantities  and  nitrogen  compounds  in 
small  quantities.  (LABORATORY  MANUAL,  Exercise  XVII.) 

165.  Phosphorus  and  Sulphur.  —  The  two  solids,  phos- 
phorus and  sulphur,  are  often  associated  in  the  minds  of 
people  because  both  are  readily  combustible  and  have  low 
kindling  points,  and  because  they  have  been  used  together 
for  a  long  time  in  making  the  tips  of  matches.  Phosphorus 
occurs  naturally  only  in  compounds.  The  element  is  pre- 
pared artificially  from  the  hard  part  of  bones,  which  is  cal- 
cium phosphate.  Phosphorus  is  a  wax-like,  slightly  yellow 
substance  which  has  the  property  of  being  self-luminous,  — 
that  is,  it  gives  off  a  faint  light.  On  account  of  its  rapid 
union  with  oxygen  if  exposed  to  air,  it  is  kept  under  water 
in  laboratories  and  factories. 


152     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

Sulphur,  under  ordinary  conditions,  is  a  lemon-yello\v 
crystalline  solid.  It  has  been  obtained  for  centuries  from 
fissures  in  the  rocks  of  volcanic  regions.  Sicily  has  exported 
great  quantities  to  the  United  States  and  to  other  countries, . 
Extensive  subterranean  beds  of  pure  sulphur  have  recently 
been  discovered  in  Louisiana,  and  the  United  States  is  now 
exporting  more  sulphur  than  it  imports. 

Sulphur  is  burned  in  rooms  which  are  infected  by  certain 
contagious  diseases,  because  the  sulphur  oxide  formed  by  its 
combustion  destroys  disease  germs.  This  oxide  is  irritating 
if  breathed  in  small  quantities,  and  when  breathed  in  large 
quantities,  it  is  fatal. 

166.  Properties   of   Metals.  —  There  are  certain  physical 
properties  which  belong  especially  to  metals : 

Luster,  shining  surface. 

Malleability,  capability  of  being  hammered  or  rolled  into 
thin  sheets  without  breaking. 

Ductility,  capability  of  being  drawn  into  wire. 

Conductivity,  ability  to  transmit  heat  and  electricity. 

Fusibility,  capability  of  being  melted. 

No  two  metals  possess  all  these  properties  in  the  same  de- 
gree; and  the  characteristic  properties  of  each  metal  vary 
greatly,  because  of  the  effect  of  temperature  and  other  con- 
ditions. Each  of  the  metals  has  its  own  peculiar  combina- 
tion of  properties  by  means  of  which  it  can  be  identified. 
Each  metal  has  its  own  specific  gravity,  its  own  peculiar 
color,  its  own  degree  of  tenacity  and  of  elasticity,  and 
other  special  properties. 

167.  Iron.  —  At  the  present  day,  iron  in  its  various  forms 
is  the  most  important  of  the  metals.     Its  properties  make  it 
the  best  metal  for  car  rails,  steamships,  locomotives,  frames 
of  buildings,  and  machines,  all  of  which  are  necessary  to  the 
life  of  our  times. 

Wrought  iron  is  the  most  nearly  pure  of  the  commercial 
forms  of  iron.  Steel  contains  a  small  per  cent  of  carbon; 


COMMON  ELEMENTS  OF  THE  EARTH  153 

cast  iron  contains  a  larger  per  cent  of  carbon  and  some  other 
impurities.  In  these  three  forms,  iron  has  certain  properties 
in  very  different  degrees;  wrought  iron  is  most  malleable, 
steel  most  tenacious  and  elastic,  cast  iron  most  brittle. 
Chains  are  made  of  wrought  iron;  car  rails  and  knife  blades 
are  made  of  steel;  heavy  pieces  of  machinery  are  made  of 
cast  iron.  Iron  rusts  if  exposed  to  outdoor  air;  to  prevent 
rusting  it  is  often  covered  with  paint,  zinc,  or  graphite  in  the 
form  of  " blacking.0 

168.  Copper  and  Gold.  —  Copper  and  gold  are  the  only 
well-known  metals  that  occur  in  abundance  free  from 
other  elements.  They  are  said  to  occur  free  or  native. 
Copper  and  gold  have  characteristic  colors,  copper  being  dull 
red,  and  gold,  yellow;  most  of  the  other  metals  have  a  gray- 
ish color.  Both  copper  and  gold  are  rather  soft,  have  a 
high  melting  point,  and  are  malleable  and  ductile  in  a  very 
high  degree.  They  have  both  been  used  since  early  times. 
This  was  because  they  were  found  free  and  required  no 
difficult  process  of  separation  from  the  ore,  and  because 
they  could  be  hammered  into  shape  with  simple  tools. 

Gold  is  less  affected  by  the  chemical  action  of  air  and  water 
than  almost  any  other  metal,  and  it  is  not  acted  upon  readily 
by  any  common  substance.  Hence  it  is  used  the  world  over 
for  coins  and  jewelry.  As  gold  is  too  soft  to  be  used  pure 
for  such  purposes,  a  little  copper  or  silver  is  melted  with  it 
to  give  it  greater  hardness.  Such  a  mixture  of  metals  is 
called  an  alloy.  Gold  that  is  described  as  "24  carat"  is 
100  per  cent  pure  gold.  The  best  grades  of  jewelry  are  18 
carat  gold,  while  the  14  carat  is  used  for  articles  which  are 
likely  to  have  hard  wear.  United  States  gold  coins  are  90 
per  cent  gold  and  10  per  cent  copper;  they  contain  an 
amount  of  gold  equal  in  value  to  the  value  of  the  coin. 

Because  of  its  great  malleability,  gold  can  be  hammered 
so  thin  that  250,000  sheets  of  gold  leaf  are  required  to  make 
a  pile  one  inch  thick.  It  is  much  thicker  than  that,  how- 


154      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

ever,  when  used  to  cover  large  surfaces   like   the   domes 
of  buildings. 

Copper  is  of  great  use  because  it  is  a  good  conductor  of 
electricity;  many  tons  of  new  copper  wire  are  brought  into 
use  daily.  Copper  is  abundant  enough  to  be  reasonably 
cheap.  It  is  made  into  coins  of  low  denomination  the  world 
over.  In  pure  form,  it  is  rolled  into  sheets  for  covering  sur- 
faces exposed  to  air  or  water. x  A  great  amount  of  copper 
is  used  on  large  buildings,  to  cover  the  valleys  and  gutters 
in  the  roof  surface.  Copper  is  alloyed  with  tin  to  make 
bronze,  and  with  zinc  to  make  brass. 

169.  Silver.  —  Silver  has  properties  similar  to  those  of 
copper  and  gold,  but  in  different  degree.     Silver  is  not  af- 
fected by  pure  air  or  water.     In  the  air  of  houses,  however, 
it   tarnishes   somewhat,    because   such    air   often   contains 
impurities  from  furnace  or  illuminating  gas. 

Both  as  solid  and  as  plated  ware,  silver  is  useful  for  table 
articles.  It  is  not  affected  by  many  kinds  of  food,  though 
eggs  and  mustard  discolor  it  because  they  contain  compounds 
of  sulphur,  which  make  a  dark  coating  on  silver.  "Solid 
silver"  is  alloyed  with  10  or  more  per  cent  of  copper  to  give 
it  greater  durability.  United  States  silver  coins  contain  10 
per  cent  of  copper. 

170.  Aluminum.  —  The  lightest  metal  in  common  use  is 
aluminum,  or  aluminium.     Its  lightness  and  the  fact  that  it 
does  not  tarnish  in  air  or  water  make  it  useful  for  kitchen 
utensils,  aeroplane  frames,  and  parts  of  automobiles.     It  is 
a  good  conductor  of  electricity. 

171.  Mercury.  —  Mercury  is   the   only  metal  which   is 
liquid  at  ordinary  temperatures.     It  is  used  in  thermometers 
and  barometers  and  in  many  other  scientific  instruments. 
As  it  will  dissolve  gold,  it  is  used  in  stamp  mills  to  separate 
fine  particles  of  gold  from  sand  or  from  rock  dust.     The  gold 
is  finally  separated  from  the  mercury  by  distillation. 

Mercury  is  used  with  other  metals  —  as  gold,  silver,  or  tin 


COMMON  ELEMENTS  OF  THE  EARTH  155 

—  to  form  soft  alloys  called  amalgams.  An  amalgam  of 
silver  and  mercury  is  used  by  dentists  in  filling  cavities  in 
teeth.  , 

172.  Uses  of  other  Metals.  —  Nickel  is  used  as  a  plat- 
ing material  and  in  coins.    Zinc,  tin,  and  lead,  in  thin  sheets, 
are  used  to  cover  wood  and  to  line  tanks.     Iron  coated  with 
zinc  is  called  galvanized  iron;  covered  with  tin,  it  is  called 
tin  plate.     Ordinary  tinware  is  thin  sheet  iron  coated  with 
tin;   the  coating  makes   the   ware    brighter    and  prevents 
rusting.     The   flexibility   of  lead  makes  it  useful  in  pipes 
which  must  be  bent  to  turn  corners.     Ordinary  water  pipes 
and  gas  pipes  are  made  of  iron,  plain  or  galvanized.     Coil 
pipes  are  frequently  made  of  copper. 

Platinum  is  one  of  the  rarest  and  most  expensivt  metals. 
Its  principal  use  is  in  scientific  apparatus  and  in  the  setting 
of  precious  stones.  Magnesium  burns  with  a  brilliant  light 
of  great  chemical  energy  and  is  therefore  used  in  photo- 
graphic flashlight  work. 

173.  The    Specific    Gravity    of    Metals.  — Most  of  the 
metals  have  a  greater  specific  gravity  than  the  common  rocks. 
The  specific  gravity  of  common  rocks  varies  from  about  2.5 
to  3.5.    Below  are  given  the  specific  gravities  of  some  of  the 
metals  in  the  pure  state: 


Platinum  21.5 

Silver       10.5 

Tin                 7.3 

Gold           19.3 

Copper      8.9 

Zinc                7.1 

Mercury    13.6 

Nickel       8.9 

Aluminum      2.6 

Lead          11.4 

Iron           8.0 

Magnesium    1.8 

174.  Chemical  Symbols.  —  In  scientific  work,  abbrevia- 
tions are  used  to  represent  the  elements.  As  many  of  the 
elements  have  Latin  names,  the  abbreviations  or  sym- 
bols may  be  unlike  their  English  names;  for  instance,  Au 
stands  for  gold,  from  the  Latin  word  for  gold,  aurum. 
In  every  language  the  symbols  used  in  scientific  work  are 
the  same. 


156     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

A  single  symbol,  whether  alone  or  combined  with  others, 
stands  for  one  atom,  which  is  the  name  chemists  have  given 
to  the  smallest  portion  of  matter  which  enters  into  com- 
bination. For  example,  Na  stands  for  one  atom  of  sodium. 
NaCl  means  that  there  is  one  atom  of  sodium  united  with 
one  atom  of  chlorine. 

Two  or  more  atoms  make  a  molecule.  If  the  atoms  are 
all  of  the  same  kind,  they  form  the  molecule  of  an  element. 
If  unlike,  they  make  a  molecule  of  a  compound.  H2  (read 
"H  two")  represents  a  molecule  of  the  element  hydrogen; 
H2O  (read  "H  two  O"),  a  molecule  of  the  compound  water. 

Below  are  the  names  and  symbols  of  some  of  the  well-known 
elements:  > 


aluminum  . 
bromine  .  . 
calcium  .  .  . 
carbon 
chlorine  .  .  . 

.  Al 
.  Br 
Ca 
.  C 
Cl 

gold    
hydrogen 
iodine     
iron  
lead  .           .    . 

Au 
H 
I 
Fe 
Pb 

mercury  .  . 
nickel  
nitrogen  .  . 
oxygen  .  .  . 
phosphorus  . 

copper    .  . 

.  Cu 

magnesium    .  . 

Mg 

platinum  .  . 

Ni  silver  ....  Ag 

N  sodium  .  .  Na 

O  sulphur  .  .  S 

P  tin Sn 

Pt  zinc          .   Zn 


EXERCISES 

1.  Why  does  one  end  of  a  match  "light"  and  the  other  not,  with 
the  same  treatment? 

2.  Why  is  iron  in  its  various  forms  the  most  important  metal  at  the 
present  day? 

3.  Why  is  iron  often  covered  with  paint,  zinc,  or  graphite? 

4.  What  weight  of  gold  is  there  in  an  18  karat  gold  ring  weighing 
25  g.? 

6.   What  properties  of  gold  make  it  useful  in  dentistry? 

6.  Compare  the  weights  of  one  cubic  centimeter  of  gold  and  of  one 
cubic  centimeter  of  a  12  karat  gold-and-copper  alloy. 

7.  In  ancient  times,  a  goldsmith  used  an  alloy  in  making  an  article 
that  was  supposed  to  be  made  of  pure  gold.     A  philosopher  detected 
the  cheating  by  weighing  the  article  in  air  and  then  in  water.     Explain 
his  method. 

8.    1,000  cu.  cm.  of  hydrogen  gas  weigh  about  yy  of  a  gram.     What 
is  the  weight  of  an  equal  volume  of  air? 


COMMON  ELEMENTS  OF  THE  EARTH  157 

9.   A  toy  balloon  has  a  capacity  of  10,000  cu.  cm.     What  weight 
of  air  will  it  displace? 

10.  Could  the  hydrogen  balloon  be  weighed  in  the  ordinary  way 
with  platform  scales  or  a  spring  balance?     Why? 

11.  Select  and  write  the  symbols  of  all  the  elements  that  you  know 
to  be  gases. 

12.  Write  the  symbols  of  all  the  elements  that  you  know  to  be  metals. 


CHAPTER  XIII 
SOME    COMPOUNDS    OF    COMMON    ELEMENTS 

175.  Chemical   Formulas.  —  A  chemical  formula  is  a  col- 
lection of  symbols  representing  the  kinds  and  the  relative 
amounts  of  the  elements  in  a  given  compound.     For  example, 
CO2  is  the  formula  for  carbon  dioxide  and  indicates  that  a 
molecule  of  this  compound  is  made  up  of  one  atom  of  carbon 
and  two  of  oxygen  chemically  united.     NaCl  is  the  formula 
for  common  salt. 

176.  Chemical    Analysis.  —  It  is  often  necessary  to  find 
out  what  substances  are  present  in  food,  medicine,  explosives, 
and  construction  materials.     The  process  by  which  this  is 
done  is  called  chemical  analysis.     A  complete  analysis  dis- 
covers what  elements  and  compounds  are  present  and  in 
what  amounts.     Laboratories  are  established  by  the  govern- 
ment, by  scientific  schools,  and  by  private  enterprises  for 
the  purpose  of  learning  the  composition  of  different  forms  of 
matter.     Manufactories  maintain  their  own  laboratories  to 
examine  raw  materials  purchased  for  their  use. 

A  test  is  an  examination  of  a  substance  to  find  out  if  a 
certain  element  or  compound  is  present.  A  test  is  not 
analysis  but  may  be  used  to  show  whether  the  conclusions 
drawn  from  the  work  of  analysis  are  correct. 

To  apply  a  test,  one  must  know  how  the  given  element  or 
compound  behaves  under  given  conditions  and  then  apply 
those  conditions  to  the  substance  under  examination.  For 
example,  if  any  compound  of  copper  is  present  in  a  solution, 
the  addition  of  ammonia  gives  a  deep  blue  color.  Knowing 
this  fact,  we  may  test  a  given  solution  to  see  if  it  contains 

158 


SOME  COMPOUNDS  OF  COMMON  ELEMENTS      159 

copper.     We  add  ammonia;    if  the  solution  then  becomes 
deep  blue,  we  know  that  copper  is  present. 

177.  Classes  of  Compounds.  —  A  class  of  compounds  in^ 
eludes  several  substances  which  resemble  one  another  either 
in  their  constituents  or  in  their  chemical  properties,  or  both. 
For  example,  all  substances  which  consist  of  oxygen  and  only 


FIG.  78.  —  BENJAMIN  SILLIMAN:    CHEMIST.     1779-1864 

By  his  lectures  delivered  in  every  part  of  the  country,  he  contributed, 
in  a  large  degree,  to  the  promotion  of  a  love  of  science  and  to  the  founda- 
tion of  scientific  institutions.  —  DANIEL  COIT  OILMAN  in  Leading  American 
Men  of  Science.  * 

one  other  element  are  oxides.  Besides  the  oxides,  there  are 
three  other  important  classes  of  common  compounds :  acids, 
bases,  and  salts. 

178.  The  Two  Most  Important  Oxides.  —  Water,  which 
is  a  hydrogen  oxide,  and  carbon  dioxide  are  compounds  which 
are  absolutely  necessary  to  living  things.  Naturally,  both 
are  provided  as  a  part  of  the  earth  itself.  Besides  being 


160     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

necessary  to  life,  water  is  useful  to  man  in  a  greater  number 
of  ways  than  any  other  liquid. 

The  amount  of  carbon  dioxide  in  the  air  is  practically  con- 
stant. Respiration  of  plants  and  animals,  the  decay  of 
plant  and  animal  substances,  and  combustion  are  con- 
stantly giving  carbon  dioxide  to  the  air.  Green  plants  are 
constantly  removing  carbon  dioxide  from  the  air. 

As  the  plant  grows,  it  uses,  in  preparation  of  its  food 
materials,  the  carbon  which' it  gets  from  the  carbon  dioxide, 
and  sets  free  the  oxygen.  As  the  oxygen  which  the 


Animals 


Pbnts 


Oxygen 

FIG.  79.  —  RELATION  OF  CARBON  DIOXIDE  TO  LIVING  THINGS 

1.  Arrow  points  indicate  the  direction  of  reading.  Begin  with  animals 
and  write  fully  what  this  diagram  tells.  2.  Begin  with  oxygen  and  write 
the  short  story. 

plant  releases  is  the  only  source  of  renewed  supply,  it  is 
plain  that  if  it  were  not  for  the  work  of  plants  on  carbon 
dioxide,  the  quantity  of  oxygen  in  the  air  would  be 
exhausted. 

179.  Acids.  —  Acids  are  compounds  which  in  water  solu- 
tions have  a  sour  taste.  They  always  contain  hydrogen, 
and  when  they  act  chemically  on  metals,  the  hydrogen  is 
usually  given  off.  The  dissolving  of  a  metal  by  an  acid  is 
not  a  mere  physical  change,  as  when  water  dissolves  sugar, 
but  is  a  chemical  change.  The  metal  takes  the  place  of 
the  hydrogen  in  the  acid-molecule,  forming  a  new  compound 
called  a  salt. 

A  simple  test  for  an  acid  is  that  it  turns  blue  litmus  paper 


SOME  COMPOUNDS  OF  COMMON  ELEMENTS      161 

red.  Litmus  paper  is  paper  colored  by  a  dye  from  a  certain 
plant.  This  dye  changes  from  blue  color  to  red  when  in 
contact  with  even  the  vapor  or  fumes  of  an  acid. 

The  most  common  acids  used  in  the  industries  are  hydro- 
chloric acid  (also  called  muriatic),  sulphuric  (called  oil  of 
vitriol),  and  nitric  acid.  In  full  strength  these  acids  are 
injurious  to  the  flesh  and  the  clothing.  They  may  be  diluted 
with  water  and  in  very  dilute  form  are  harmless.  Sulphuric 
acid  is  used  in  making  most  of  the  other  acids. 

Other  acids,  such  as  oxalic,  tartaric,  and  citric,  are  found  in 
dilute  forms  in  the  juices  of  fruits  and  leaves  of  plants.  Acetic 
acid  is  formed  when  cider  " works"  or  ferments,  and  it  is  the 
acid  which  gives  vinegar  its  sour  taste. 

180.  Bases.  —  In  general,  bases  are  opposite  to  acids  in 
their  properties.     Their  solutions  turn  red  litmus  paper  blue. 
Ammonium    hydroxide    (called    ammonia    water),    sodium 
hydroxide   (called    caustic   soda),    and    calcium    hydroxide 
(called  slaked  lime)  are  bases. 

Most  burns  and  stings  of  insects  are  painful  because  of 
an  acid  formed  by  the  burn  or  injected  in  the  stinging. 
The  application  of  certain  basic  materials,  such  as  soap, 
cooking  soda,  or  lime  water,  counteracts  the  acid  and  thus 
affords  relief. 

181.  Salts.  —  If  an  acid  and  a  base  are  put  together  in 
the  right  proportions,  the  characteristic  properties  of  both 
disappear.     Since  the  product  is  neither  an  acid  nor  a  base, 
it  is  said  to  be  neutral.     If  the  water  is  evaporated  from 
the  resulting  solution,  there  remains  a  crystalline  or  powdered 
solid  called  a  salt,  which  is  not  like  either  the  acid  or  the 
base. 

Nearly  all  minerals  are  salts.  Most  of  these  salts  found  in 
the  rocks  are  only  slightly  soluble.  The  more  soluble  salts 
are  dissolved  by  the  water  which  is  continually  washing  over 
and  through  the  earth's  crust,  and  are  carried  finally  into 
the  ocean.  Since  this  has  been  going  on  through  all  the  ages, 


162     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

most  of  the  soluble  salts  are  by  this  time  in  the  springs,  lakes, 
and  oceans. 

The  most  abundant  salt,  which  is  the  chief  one  in  the 
ocean,  is  our  common  table  salt.  Its  chemical  name  is 
sodium  chloride,  because  it  contains  sodium  and  chlorine. 
It  is  a  good  example  of  salts,  and  the  terms  which  describe  it 
would,  with  slight  variation,  describe  many  salts.  Color, 
degree  of  solubility,  and  the  form  of  the  crystal  are  important 
physical  properties  of  salts.  (LABORATORY  MANUAL,  Exer- 
cise XVIII.) 

182.  Some  Uses  of  Salts.  —  Besides  the  familiar  table 
salt,  there  are  many  other  salts  which  are  used  in  manufac- 
turing. 

Copper  sulphate  is  a  blue  salt,  commonly  called  blue 
vitriol.  With  water,  it  makes  a  blue  solution  which  is  used 
in  electric  batteries  and  in  copper  plating. 

Silver  chloride  and  silver  bromide  are  used  in  photography, 
because  light  acts  upon  them  chemically.  The  film  or  plate 
in  the  camera  has  a  coating  of  one  of  these  salts.  The  light 
which  comes  through  the  camera  lens  during  the  exposure 
acts  upon  the  silver  compound.  Since  the  light  falling  on 
the  film  is  stronger  in  some  places  than  in  others,  the  salt 
is  affected  in  different  degrees  in  different  places,  exactly 
corresponding  with  the  degree  of  light  from  the  objects 
outside.  To  make  this  effect  visible,  the  film  or  plate  is 
developed  by  treating  it  with  solutions  of  various  other 
salts.  Developing  completes  the  chemical  action  begun  by 
light.  Then  another  solution,  the  fixing  bath,  is  used  to 
remove  all  the  silver  compounds  which  have  not  been  acted 
upon  by  light,  and  the  negative  is  complete.  It  is  on 
account  of  this  chemical  effect  of  light  on  silver  compounds 
that  photography  is  possible. 

Solutions  of  salts  containing  gold,  silver,  and  nickel  are 
used  in  electroplating  table  utensils,  jewelry,  and  parts  of 
machines. 


SOME  COMPOUNDS  OF  COMMON  ELEMENTS      163 

183.  Carbonates.  —  Carbonates  are  salts  containing  va- 
rious metals  combined  with  carbon  and  oxygen.  Sodium 
carbonate  is  the  common  washing  soda,  and  calcium  car- 
bonate is  the  compound  of  which  limestone  and  marble 
are  composed.  Sodium  and  potassium  carbonates  are 
much  used  in  the  preparation  of  soaps  and  washing 
powders,  because  they  change  fats  and  grease  to  soluble 
substances. 

Carbonates  are  valued  because  by  simple  treatment  car- 
bon dioxide  gas  can  be  procured  from  them.  Any  car- 


Battery  i 


FIG.  80.  —  A  SILVER  PLATING  BATH 

The  tank  contains  a  solution  of  some  compound  of  silver.  One  wire 
from  the  battery  connects  with  a  bar  of  silver,  and  the  other  wire  with  a 
spoon  which  is  to  be  plated.  1.  Starting  with  the  positive  electrode  of  the 
battery,  name  all  the  parts  of  the  circuit.  2.  When  a  current  is  passing, 
molecules  of  silver  leave  the  solution  and  cling  to  the  spoon.  Their  places 
in  the  solution  are  taken  by  molecules  from  the  bar  of  silver.  Which 
way,  then,  does  the  current  go  in  the  plating  solution? 

bonate  decomposes  on  the  addition  of  even  a  weak  acid, 
giving  off  carbon  dioxide. 

Sodium  bicarbonate  is  used  in  the  preparation  of  some 
foods.  Baking  powder  consists  of  a  dry  carbonate  mixed 
with  a  weak  acid  in  powder  form.  As  long  as  both  sub- 
stances are  dry,  they  do  not  affect  each  other;  but  as  soon 
as  they  are  dissolved  in  water  or  milk,  they  act  on  each 


164     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

other  chemically  and  carbon  dioxide  is  set  free.  While  this 
gas  is  rising  through  the  dough,  cooking  stiffens  the  material 
and  it  remains  porous,  making  biscuit,  cake,  and  pastry 
"light." 

184.  Fertilizers.  —  Plants,  during  their  growth,  are  con- 
tinually removing  from   the   soil   certain   salts  which   are 
needed  for  their  food.     In  forests  and  uncultivated  lands, 
the  plants  die  and  decay  in  the  ground,  and  thus  all  the  salts 
are  returned  to  the  soil.     But  on  farms  the  plants  are  re- 
moved when  they  are  grown,  and  are  used  as  food  for  animals 
or  men.     Moreover,  rain  dissolves  some  of  the  salts  of  the 
soil  and  carries  them  away  to  sea.     In  these  ways,  the  salts 
needed  for  plant  growth  are  continually  removed  from  the 
soil  and  are  not  returned  to  it. 

It  is  easy  to  see  that  if  this  loss  continued,  the  fertility  of 
the  soil  would  soon  be  exhausted,  and  it  would  be  impossible 
to  grow  crops.  The  loss  may  be  made  good,  however,  by 
the  use  of  fertilizers.  These  are  combinations  of  salts  to 
replace  the  material  taken  from  the  soil. 

Fertilizers  may  be  mineral  or  organic.  A  mineral  fertili- 
zer is  one  which  is  obtained  directly  from  rocks  or  earthy 
deposits.  An  organic  fertilizer  is  decaying  vegetable  or  ani- 
mal matter.  Calcium  phosphate,  from  the  great  beds  of 
fossil  bones  near  the  coast  in  North  and  South  Carolina,  has 
long  been  a  source  of  phosphates  for  fertilizers.  Guano  (the 
excrement  of  various  kinds  of  marine  birds)  is  found  in  ex- 
tensive beds  on  islands  off  the  coast  of  Peru  and  Chili. 
Guano  contains  phosphates  and  nitrogen  compounds,  both 
of  which  are  used  as  foods  for  plants. 

185.  The   Science  of  Agriculture.  —  The  composition  of 
soils  is  learned  by  analysis  made  in  the  laboratories  and  fields 
of  agricultural  colleges  and  of  the  Unites  States  Department 
of  Agriculture.     By  analysis  it  is  possible  to  determine  also 
what  compounds  are  needed  in  the  soil  for  certain  crops. 
Grass,  corn,  and  potatoes  each  has  its  own  needs,  and  the 


SOME  COMPOUNDS  OF  COMMON  ELEMENTS       165 

same  fertilizer  will  not  prepare  the  soil  equally  well  for  all 
of  them.  The  preparation  of  artificial  fertilizers  is  a  great 
industry. 

The  study  of  the  needs  of  the  soil  and  of  crops  has  been 
of  great  benefit  to  mankind.  It  is  not  the  farmers  alone 
who  are  benefited,  for  the  whole  world  depends  on  the  suc- 
cess of  crops  for  its  daily  food. 


FIG.  81.  —  EFFECT  OF  FERTILIZERS  UPON  CROPS 

This  is  a  picture  of  potato  harvesting  in  the  state  of  Maine,  which  in 
some  parts  has  a  natural  soil  adapted  to  the  needs  of  the  potato.  The 
average  yield  for  the  whole  United,  States  is  92  bushels  per  acre.  A  .good 
yield  in  "  the  potato  county  "  (Aroostook,  Maine)  is  275  bushels  per  acre. 
By  the  use  of  fertilizers  well  adapted  to  the  soil  and  the  crop,  a  yield  of  462 
bushels  per  acre  was  obtained  from  this  field  in  the  same  "  potato  county." 

186.  Poisons.  —  A  poison  is  a  substance  which  produces 
serious  illness  if  taken  into  the  body.  An  antidote  is  a  sub- 
stance given  to  remove  the  poison  or  overcome  its  effect. 
The  value  of  an  emetic  lies  in  its  power  to  remove  the  poison 
quickly  from  the  stomach.  In  most  cases  of  poisoning,  good 
antidotes  are  milk  and  raw  eggs,  especially  the  raw  white  of 


166     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

eggs.  In  all  cases  a  physician  should  be  called  at  once  and 
the  more  powerful  antidotes  should  be  given  only  under  his 
direction. 

Many  antiseptics  and  disinfectants  which  are  used  to  kill 
disease  germs,  will  kill  people  also  if  taken  internally.  Cor- 
rosive sublimate,  carbolic  acid,  formaldehyde,  and  other  poi- 
sonous compounds  are  commonly  used  as  disinfectants. 
They  should  be  plainly  marked  POISON  and  kept  where  they 
cannot  be  used  accidentally. 

EXERCISES 

1.  (a)  State  five  physical  properties  of  water.     (6)  Which  of  these 
do  you  think  would  be  very  important  in  chemical  work?     Why? 

2.  Name  four  uses  of  water  besides  those  of  the  home  and  the  farm. 

3.  Name  four  uses  of  carbon  dioxide.     State  one  which  depends 
upon  a  chemical  property. 

4.  Is  there  carbon  dioxide  in  baked  bread?     Why? 

5.  Is  there  carbon  dioxide  in  cider?     Why? 

6.  What  relation  is  the're  between  acids,  bases,  and  salts? 

7.  What  is  meant  by  the  expression,  "One  substance  neutralizes 
the  effect  of  another"? 

8.  What  substance  might  neutralize  the  chemical  effect  of  ammonia 
solution? 

9.  What  substance  might  remove  a  spot  made  upon  blue  cloth  by 
lemon  juice? 

10.   Why  is  sulphuric  acid  the  most  important  of  all  acids? 


CHAPTER  XIV 
MINERALS   AND    ORES;    THEIR   VALUE   AND    SOURCE 

187.  The  Crust  of  the  Earth.  —  The  solid  outside  part 
of  the  earth  is  composed  of  rock.  This  is  covered  in  most 
places  by  a  layer  of  mantle  rock,  a  fine  material  consisting  of 


1.  Oxygen  50$  5.  Calcium  6# 

2.  Silicon  25$  6.  Magnesium  1.3j£ 

3.  Aluminum  8#  7    Sodium  H 

4.  Iron  7$  8*.  Potassium  1* 

9.   Ail  others  less  than  \<fr 

FIG.  82.  —  PERCENTAGE  OF  ELEMENTS  IN  ROCKS 

1.  What  element  abundant  in  living  matter  is  not  included  in  this 
diagram?  2.  About  how  many  elements  are  known?  3.  How  many 
elements  must  then  be  included  in  the  "less  than  1  %"  ? 

soil  together  with  sand,  gravel,  or  clay,  which  has  generally 
been  made  from  the  rocks  which  it  now  covers. 

188.   Minerals.  —  Rocks  consist  of  minerals.     A  mineral 
is  sometimes  an  element,  but  more  often  it  is  a  definite  com- 

167 


168     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


pound  of  two  or  more  elements.  The  five  most  abundant 
elements  in  minerals  are  oxygen,  silicon,  aluminum,  iron, 
and  calcium.  Many  others  exist  in  small  quantity. 

Minerals  differ  in  color,  hardness,  solubility,  and  fusibility, 
and  in  the  form  of  their  crystals.  A  crystal  is  a  body  of 
definite  form,  having  a  number  of  flat,  lustrous  surfaces. 
Crystals  are  formed  from  the  cooling  of  a  melted  substance 
or  the  evaporation  of  a  solution.  Every  mineral  has  its  own 
form  of  crystal. 

189.  Ores.  —  An  ore  is  a  mineral  which  is  valued  for  the 
metal  that  can  be  obtained  from  it.  Iron  ore  is  a  compound 

of  iron  and  other  elements, 
one  of  which  is  often  oxygen. 
Many  ores,  as  those  of  sil- 
ver, lead,  and  zinc,  are  com- 
pounds of  sulphur  and  the 
metal.  Most  minerals  con- 
tain a  small  amount  of 
metal,  but  minerals  are  not 
classed  as  ores  unless  it  is 
profitable  to  separate  the 
metal  from  the  other  ele- 
ments with  which  it  is  com- 
bined. 

190.  Reduction  of  Ores. 
-  By  reduction  of  an  ore 
is  meant  the  separation  of 
the  metal  from  its  com- 
pounds and  from  the  rock 
with  which  the  compounds  are  mixed.  The  compound  is 
said  to  be  reduced,  and  the  material  which  produces  the 
separation  of  the  metal  is  called  the  reducing  agent. 

If  chemical  solvents  are  to  be  used  to  remove  the  metal, 
the  ore  is  first  crushed  under  huge  weights  or  hammers,  called 
stamps.  It  is  then  submitted  to  the  action  of  chemicals 


FIG.  83.  —  QUARTZ  CRYSTALS 

When  solutions  of  minerals  evapo- 
rate slowly,  or  when  melted  substances 
cool  slowly,  crystals  of  various  sizes 
form.  Whatever  the  size,  the  faces  are 
planes.  In  crystals  of  a  given  mineral, 
corresponding  faces  always  make  the 
same  angle  with  each  other. 


MINERALS  AND  ORES 


169 


o  — 


which,  by  solution,  remove  the  metaj  from  the  ore.     If  heat 

is  to  be  the  chief  reducing  agent,  the  ore  may  be  used  in 

larger  lumps.     These  lumps  are 

put  into  a  tall,  cylindrical  blast 

furnace.      A    blast    furnace    is 

made   in  such   a   way   that    a 

powerful    blast   of  air   can    be 

forced  through  it  to  secure  rapid 

combustion  and  therefore  a  very 

high  temperature. 

The  reduction  of  iron  is  ac- 
complished as  follows:  Layers 
of  coal  or  coke,  ore,  and  lime- 
stone are  built  up  within  the 
furnace  to  about  two  thirds  its 
height,  and  the  fuel  is  ignited. 
Since  the  fuel  and  ore  are  ar- 
ranged in  layers,  the  fire  is  not 
confined  to  the  bottom  of  the 
furnace,  but  extends  all  through 
the  mass.  On  the  top,  as  the 
mass  settles  down,  new  material 
is  added  from  time  to  time. 
The  rock  material  of  the  ore 
and  the  limestone,  which  is 
called  a  flux,  melt  and  unite 
to  form  a  glass-like  substance,  FIG>  34.  _  A  BLAST  FURNACE 
known  as  slag.  w  =  wall  Hned  ^  fire  day . 

When      the     rock     has      been    /  and   o  =  fuel,    flux,    and    ore; 

separated  from  the.  ore,  what    U^oX^^odtS 

remains     is      chiefly     the     Oxide     waste  gases  which  are  used  to  heat 
Of     iron.      The    heating    is    COn-     the  air  blast  6,  which  enters  near 

the  base;    s  =  slag;    m  =  melted 

tinued,   and  the  hot  carbon  of    iron. 
the   fuel  unites  with  the  oxy- 

gen   of   the   iron   Oxide,   forming     nace,  whence  they  are  drawn  out. 


170       FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

oxides  of  carbon  and  leaving  the  iron  nearly  pure.  The 
melted  metal  sinks  to  the  bottom  of  the  furnace  and  the 
slag,  being  lighter  than  the  metal,  floats  upon  it.  At 
intervals  each  is  drawn  off  through  .openings  in  the  side 
of  the  furnace.  The  iron  runs  into  trenches  in  sand,  where 
it  cools  in  bars,  and  these  bars  are  then  broken  into  con- 
venient lengths  called  "pigs." 

191.  Gems.  —  Gems  are  minerals  valued  for  their  beauty. 
This  quality  of  beauty  depends  on  color,  hardness,  and  bril- 
liance.    The  color  is  often  due  to  a  slight  trace  of  some  metal 
present  as  an  impurity,  like  a  stain,  which  is  not  a  part  of  the 
compound. 

"Precious  stones,"  or  jewels,  are  cut  from  gem  stones, 
which  are  usually  crystals.  A  jewel  is  generally  very  much 
smaller  than  the  crystal  from  which  it  is  cut,  because  only  a 
part  of  the  crystal  has  the  clear,  uniform  color  desired  and 
much  has  to  be  cut  away.  The  chips  are  used  for  jewels  in 
watches  and  for  ornamental  settings  of  other  stones.  As  the 
diamond  is  the  hardest  gem,  diamond  chips  are  often  bedded 
in  a  metal  tool  for  cutting  other  gems  or  glass. 

192.  Quartz.  —  The  most  abundant  minerals  are  quartz, 
feldspar,   mica,   and  calcite.     Quartz,   also  called  silica,  is 
composed  of  the  two  elements,  silicon  and  oxygen.     It  occurs 
in  different  forms  and  colors,  and  so  has  many  names.     Rock 
crystal  is  a  kind  of  quartz  that  is  colorless  and  transparent; 
amethyst  is  a  crystal  of  purple  color;    agate  is  of  various 
colors,  sometimes  in  bands;    and  flint  is  dark  and  horny 
looking.     Rock  crystal  and  amethyst  are  in  the  crystalline 
form ;  the  others  are  not.     All  have  the  same  degree  of  hard- 
ness, insolubility  in  water  and  acids,  and  infusibility  in  fire. 
Quartz  is  therefore  a  very  durable  mineral.     Quartz  melts 
if  mixed  with  soda  or  potash  and  heated  to  a  high  tem- 
perature, and  the  product  is  common  glass.     Finer  grades 
of  glass  and  colored  glass  are  made  by  adding  other  mineral 
compounds. 


MINERALS  AND  ORES 


171 


193.  Feldspar.  —  Feldspar  contains  the  same  elements  as 
quartz  and,  in  addition,  the  elements  of  lime  or  soda  and  of 
alumina  (a  very  hard  mineral,  sometimes  known  as  corundum 
or  emery).  Feldspar  is  not  so  hard  as  quartz,  is  fusible,  and 
on  being  exposed  to  the  air  crumbles  to  clay.  Clay  is  found 
in  many  soils,  where  it  furnishes  some  elements  required  by 


FIG.  85.  —  JAMES  DWIGHT  DANA:    GEOLOGIST.     1813-1895 

The  characteristic  that  most  impressed  all  who  came  to  know  him, 
whether  through  the  reading  of  his  works  or  through  personal  intercourse, 
was  his  profound  sense  of  the  sacredness  of  truth.  .  .  .  Even  to  extreme 
old  age  he  remained  hospitable  to  new  truth  and  ready  to  change  opinions. 
Disloyalty  to  truth  was  infidelity  to  God.  In  his  scientific  investigations 
he  always  felt,  like  Kepler,  that  he  was  thinking  God's  thoughts  after  him. 
—  WILLIAM  NORTH  RICE  in  Leading  American  Men  of  Science. 

plants.     Because  of  its  fusibility,   feldspar  is  common  in 
volcanic  rocks;  these  rocks  on  decaying  make  fertile  soil. 

Common  crockery  is  made  from  white  clay,  pressed  into 
shape  and  baked.  Powdered  feldspar  is  used  to  make  the 
glazing  for  the  surface.  There  are  feldspar  quarries  in 


172      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

Connecticut  from  which  the  crushed  mineral  is  shipped  to 
various  potteries  in  New  York  and  New  Jersey. 

194.  Mica.  —  Mica  has  a  composition  similar  to  feldspar, 
but  it  has  different  properties.     It  is'  usually  gray  or  very 
dark  in  color,  and  breaks  into  thin  sheets,  which  are  almost 
transparent  and  are  very  tough.     It  does  not  decompose 
as    readily    as    feldspar.      The    shining    scales    found    in 
sand  and  sandstone  are  mica.      Sheets  of  mica,  commonly 
called  isinglass,  are  used  in  the  doors  of  stoves,   because 
mica  is  not  affected  by  the  heat  and  the  fire  can  be  seen 
through  it. 

195.  Hornblende.  —  Hornblende  is  another  mineral  simi- 
lar to  feldspar  in  composition.     Very  small  pieces  of  horn- 
blende often  look  like  mica.     Unlike  mica,  however,  it  is 
brittle  and  does  not  split  into  thin  layers.     It  has  various 
colors  and  forms.     One  kind,  called  asbestos,  is  fibrous;   its 
threads  are  made  into  a  kind  of  paper  or  cloth.     Asbestos  is 
used  to  protect  surfaces  from  heat,  because  it  is  non-com- 
bustible and  infusible  and  is  also  a  non-conductor  of  heat. 
It  is  often  used  for  a  covering  to  furnace  and  steam  pipes, 
to  prevent  the  radiation  of  heat  from  the  pipes. 

Quartz,  feldspar,  and  either  mica  or  hornblende  are  the 
minerals  which  compose  the  great  class  of  rocks  known  as 
granite. 

196.  Calcite.  —  Calcite,  or  carbonate  of  lime,  is  the  name 
of  a  mineral  composed  of  calcium,  carbon,  and  oxygen.     It  is 
sometimes  found  in  the  fornTof  clear,  transparent  crystals, 
but  more  often  it  occurs  in  an  opaque,  non-crystalline  form 
called  limestone.     Limestone  is  white  or  gray,  and  is  much 
softer  than  quartz.     On  being  heated,  it  gives  off  carbon 
dioxide  and  leaves  lime. 

Limestone  is  soluble  in  water  in  which  carbon  dioxide  has 
been  dissolved.  Rain  water  that  has  passed  through  the 
soil  contains  dissolved  carbon  dioxide  obtained  from  the  air 
and  the  decay  of  plants.  As  this  water  flows  over  and 


MINERALS  AND  ORES 


173 


FIG.  86.  —  IN  THE  CAVE  OF  THE  WINDS,  MANITOU,  COLORADO 

This  cave  has  been  made  in  limestone  rock  by  water  which  has  trickled 
through  and  dissolved  the  calcium  carbonate.  1.  What  name  is  given  to 
the  hanging  masses?  2.  How  are  the  masses  on  the  floor  formed?  3.  In 
what  respect,  beside  form,  do  they  differ  from  thp  roof  and  sides  of  the 


through  limestone,  it  dissolves  some  of  the  rock,  leaving 
crevices  and  sometimes  large  caverns.  Later,  as  the  water 
trickles  through  the  roofs  of  such  caverns,  some  of  the  water 
evaporates  and  leaves  limestone  pendants  of  crystallized  cal- 
cite,  hanging  like  icicles  from  the  roof.  The  falling  drops 
leave  on  the  floor  a  deposit  of  limestone  which  gradually 
accumulates  and  makes  a  little  mound.  The  pendants  are 
stalactites,  and  the  mounds  are  stalagmites.  They  extend 
toward  each  other,  until  they  meet  and  gradually  form  a 


174      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

column,  which  increases  in  size  as  the  trickling  water 
deposits  more  and  more  material.  The  Mammoth  Cave 
in  Kentucky,  the  Luray  Caverns  in  Virginia,  and  the 
caves  of  the  cliff  dwellings  in  Colorado  are  the  result  of 
the  dissolving  and  removing  of  limestone  rock  by  under- 
ground waters. 

197.  Marble.  —  Calcite  which  has  been  changed  from  the 
ordinary  form  of  limestone  to  a  crystalline  condition  is  called 
marble.     A  broken  piece  of  marble  has  a  glistening  look, 
because  every  face  of  the  tiny  crystals  of  which  it  is  com- 
posed is  smooth  and  shining.     The  Washington  Monument 
and  many  public  buildings  at  the  national  capital  are  built 
of   coarse-grained   marble.     Statuary   is   made   of   a   finer 
grained  marble,  free  from  stains.     The  marble  quarried  at 
Carrara,  Italy,  is  highly  prized  for  this  purpose.     Most  of 
the  marble  used  for  building  in  the  United  States  is  from 
Vermont;  quarries  in  Tennessee  furnish  much  of  our  marble 
for  interior  use. 

198.  Gypsum.  —  Gypsum  is  a  sulphate  of  lime.     It  is  a 
white  mineral  which  is  found  dissolved  in  sea  water  and  is  de- 
posited after  the  water  evaporates.    It  is  sometimes  found  in 
large  masses  of  rock.     When  fine  and  translucent,  it  is  called 
alabaster,  and  is  used  for  ornaments.     A  coarser  kind  of  gyp- 
sum, on  being  heated,  crumbles  to  a  powder,  which  is  called 
plaster  of  Paris.     This  is  used  extensively  as  a  wall  finish. 
If  water  is  added  to  the  plaster,  it  soon  hardens  into  a  solid 
mass.     In  this  way,  it  is  used  by  artists  to  make  plaster  casts, 
and  by  surgeons  to  form  a  rigid  support  for  a  broken  limb. 

199.  Petrifactions.  —  When   plants    and    animals    decay 
under  the  ground  and  in  the  presence  of  water  containing 
dissolved  mineral  matter  (such  as  silica  or  calcite),  the  min- 
eral sometimes  takes  the  place  of  the  decaying  material. 
Although  the  old  form  and  frequently  the  old  color  remain, 
a  stone  body  results.     This  is  called  a  petrifaction  or  a 
petrified  body. 


MINERALS  AND  ORES 


175 


In  some  places,  as  in  parts  of  Arizona  and  the  Yellowstone 
Park,  there  are  great  areas  covered  with  fragments  of  petri- 
fied wood  that  was  buried  for  long  ages.  Hundreds  of 
thousands  of  years  ago  a  forest  was  there.  In  the  course  of 
time,  the  trees  became  submerged,  and  while  under  water 
the  wood  decayed  and  its  molecules  were  replaced  by  mole- 
cules of  the  mineral  silica.  The  trees  were  petrified.  Later 
the  region  was  elevated;  the  surface  was  removed  by  rain, 


FIG.  87.  —  NATURAL  BRIDGE 

This  is  a  large  petrified  tree  trunk  in  the  petrffied  forest  at  Adamana, 
Arizona.  This  tree  must  have  fallen,  been  covered  with  water  containing 
silica,  and  petrified  while  submerged.  In  the  erosion  which  has  since 
occurred,  earth  has  been  taken  from  underneath,  leaving  it  across  a  gully  or 
arroyo. 

wind,  and  running  water;  and  now  stone  trunks  of  trees  and 
broken  fragments  lie  on  the  surface  of  the  sandy  plain. 

200.  Importance  of  the  Study  of  Minerals.  —  A  descrip- 
tion of  minerals,  some  of  which  we  have  never  seen,  is  rather 
uninteresting.  It  seems  of  no  use  to  know  whether  calcite 
is  soluble,  whether  feldspar  crumbles,  whether  quartz  is  hard 
or  soft.  When  we  associate  these  facts  with  others,  however, 


176      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

we  find  that  they  help  to  explain  some  very  important  and 
interesting  things  about  our  home,  the  earth.  How  the 
rocks  were  made;  where  the  material  came  from;  why  some 
rocks  are  under  water  and  some  aboye;  why  some  hills  are 
higher  than  others;  why  some  are  rounded  and  some  sharp; 
why  some  plateaus  are  deeply  cut  and  others  plain  —  these 
are  a  few  of  the  questions  that  depend,  for  their  answers,  on 
•a  knowledge  of  minerals. 

An  old  proverb  says  that  "A  chain  is  not  stronger  than 
its  weakest  link."  We  might  borrow  the  form  and  say  that 
a  rock  is  not  more  lasting  than  its  softest  mineral.  The 
hills  are  not  everlasting,  although  they  remain  apparently 
unchanged  for  many  generations  of  human  life.  The  dura- 
bility of  the  rocks  of  which  they  are  made  depends  largely 
upon  the  hardness  and  solubility  of  the  minerals  which 
compose  the  rocks. 

EXERCISES 

1.  Which  is  more  valuable,  a  gem  cut  from  rock  crystal  or  one  made 
from  amethyst?     Why? 

2.  Asbestos  may  be  woven  like  thread  or  made  into  sheets  like 
paper,  but  it  has  a  property  entirely  different  from  either  thread  or 
paper.     What  is  this  property? 

3.  For  what  purposes  is  asbestos  cloth  or  asbestos  paper  used? 

4.  What  mineral  is  a  large  constituent  of  volcanic  rocks?     Why? 

5.  The  soil  on  the  old  slopes  of  Vesuvius  is  very  fertile.     Give  a 
reason,  remembering  that  soil  is  partly  made  of  decomposed  rock. 

6.  Why  are  underground  caves  never  made  in  granite  rock? 

7.  Why  does  it  not  always  prove  profitable  to  take  the  gold  from 
a  vein? 

8.  Why  cannot  quartz,  as  well  as  feldspar,  be  made  into  pottery? 

9.  Give  directions  for  preparing  some  crystals  of  salt,  or  copper 
sulphate,  or  alum. 

10.  Explain  why  stalactites  show  a  crystalline  structure. 

11.  Arrange  the  following  in  groups,  as  rocks  or  minerals:   marble, 
agate,  iron  ore,  sandstone,  calcite,  granite,  feldspar,  limestone,  gypsum, 
quartz,  asbestos,  amethyst,  mica. 


CHAPTER  XV 


THE    CRUST    OF    THE    EARTH,    MAN'S    STOREHOUSE 

201.  The  Formation  of  the  Earth's  Crust.  —  We  do  not 

know  what  was  the  beginning  of  the  earth,  how  it  came 
to  have  a  cold  surface 
and  a  hot  interior,  or 
where  the  atmosphere 
and  the  oceans  came 
from.  But  we  do  know 
that  millions  of  years 
ago  melted  rock  was 
squeezed  out  from  the 
interior  of  the  earth  and 
became  solid  at  the  sur- 
face. The  rocks  within 
reach  of  the  water  at 
once  began  to  wear 
away,  as  the  waves  beat 
upon  them. 

Some  of  the  soluble 
minerals  composing  the 
rocks  were  dissolved,  and 


FIG.  88.  —  WATER-WORN  ROCKS 


These  rocks  have  been  acted  upon  for 
unnumbered  centuries  by  air,  water,  heat, 
and  cold.  1.  Name  a  possible  effect  of 
each  upon  the  minerals  composing  the 
rocks.  2.  Many  cracks  are  exposed; 
how  do  they  assist  in  making  frag- 
ments? 


the  insoluble  minerals 
formed  fragments  and 
grains  of  different  sizes, 
more  or  less  water- worn. 
Finally  these  fragments  were  distributed  in  beds  or  layers  by 
the  action  of  the  waves  and  currents.  The  spaces  between 
the  fragments  became  filled  with  a  cementing  substance  ob- 
tained from  the  dissolved  minerals,  and  thus  the  whole 
mass  was  consolidated  or  bound  together  into  new  rock. 

177 


178     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

In  the  course  of  time,  many  of  the  rocks  were  changed  into 
crystalline  rocks.  From  that  far-away  age  of  the  world 
even  up  to  the  present  time,  rocks  have  been,  and  still  are, 
in  the  process  of  formation. 

Rocks  are  divided,  according  to  the  way  they  were  made, 
into  three  classes:  igneous,  sedimentary,  and  metamorphic. 


FIG.  89. — A  GRANITE  QUARRY 

Observe  the  irregular  surfaces  of  the  rock  exposed,  unlike  those  of  Figs. 
90  and  91.  When  this  igneous  rock  contracted  as  it  solidified,  cracks  called 
joint  planes  were  made.  1.  What  is  their  general  direction  with  regard  to 
the  earth's  surface  ?  2.  Are  they  a  help  or  a  hindrance  to  quarrying  ? 

202.  Granite  and  other  Igneous  Rock.  —  Igneous  rocks 
are  those  which  originally  rose  in  a  melted  condition  from 
within  the  earth,  and  afterwards  cooled  either  near  the 
surface  or  often  very  far  below  it.  The  microscope  shows 
these  rocks  to  be  made  of  crystalline  grains  of  different 
sizes,  neatly  fitted  together. 


THE  CRUST  OF  THE  EARTH         179 

Granite  is  the  most  common  igneous  rock.  It  is  of 
coarse  structure  and  is  made  up  of  small  crystals  of 
quartz,  feldspar,  and  mica,  which  can  be  plainly  seen  and 
distinguished.  Granite  may  be  gray,  red,  or  pink,  varying 
according  to  the  color  of  the  feldspar.  It  is  one  of  the 
hardest  and  most  durable  of  rocks.  It  forms  a  part  of  most 
mountain  chains;  in  the  wearing  down  of  old  mountains, 
it  is  often  left  exposed,  sometimes  standing  in  peaks,  like  the 
White  Mountains  and  the  Sierra  Nevadas.  The  rocks  of 
the  New  England  coast  show  that  granite  underlies  much 
of  that  region. 

Granite  is  used  for  the  foundations  and  walls  of  buildings, 
and  for  bridges,  paving  blocks,  and  monuments.  Maine  has 
long  been  supplying  granite  to  the  country,  in  many 
varieties  of  color.  All  the  New  England  states  have  large 
quarries. 

Lava  is  a  fine-grained  igneous  rock  which  varies  greatly  in 
color.  Vesuvian  lava  is  very  dark;  the  lavas  on  the  west 
slope  of  the  Rocky  Mountains  are  light,  of  reddish-gray  color. 
In  the  eastern  states  the  lava,  which  is  called  trap  rock,  is  a 
dark  bluish-gray  and  contains  a  compound  of  iron.  Mount 
Holyoke  in  the  Connecticut  Valley  in  Massachusetts  and 
the  Palisades  of  the  Hudson  opposite  New  York  City  are 
ridges  of  hard  trap  rock. 

203.  Sedimentary  Rocks.  —  Sedimentary  or  fragmental 
rocks  are  formed  from  fragments  broken  and  worn  off  from 
older  rocks  by  the  action  of  frost,  waves,  and  wind.  These 
fragments  are  carried  by  streams  and  ocean  currents  until 
finally,  in  quiet  water,  the  sediment  falls  to  the  bottom,  form- 
ing horizontal  layers.  The  finer  fragments,  being  lighter,  are 
carried  farther  from  shore  and  thus  the  fragments  are  as- 
sorted according  to  size.  These  fragments,  in  the  course 
of  time,  are  cemented  together  in  great  beds  or  sheets. 
These  are  called  strata,  which  is  the  plural  of  the  Latin  word 
stratum,  meaning  "a  bed."  .- 


180      FIRST  YEAR   COURSE  IN   GENERAL  SCIENCE 

The  principal  sedimentary  rocks  are  conglomerates,  sand- 
stones, shales,  and  limestones. 

Conglomerates,  or  "  pudding-stones,"  are  rocks  made  from 
beds  of  sand  mixed  with  pebbles  and  stones. 


FIG.  90.  —  A  SANDSTONE  QUARRY 

Find  in  this  picture  evidence:  1.  That  layers  of  sediment  are  not  all 
of  the  same  thickness.  2.  That  these  strata  have  not  been  much  dis- 
turbed by  uplifts. 

Sandstones  are  made  from  sand  beds,  the  grains  of  which 
are  mainly  quartz.  They  are  the  most  common  rocks.  A 
well-cemented  conglomerate  or  sandstone  makes  a  very 
durable  rock.  The  so-called  brownstone,  widely  used  both 
as  building  and  as  trimming  stone,  is  a  sandstone  in  which  the 
cement  is  an  oxide  of  iron  that  gives  the  stone  a  reddish- 


THE  CRUST  OF  THE  EARTH         181 

brown  color.     Other  sandstones  are  light  colored,  the  cement 
being  silica  or  bicarbonate  of  lime. 

Shales  are  consolidated  clay  beds  or  mud  beds.  They 
often  contain  mica  flakes.  As  their  chief  mineral  is  feldspar, 
shales  decompose  readily  and  make  good  soil. 


FIG.  91. — LIMESTONE  QUARRY  NEAR.  COLUMBUS,  OHIO 

1.  Tell  what  you  can  learn  by  observation  about  the  formation  of 
this  rock  and  any  changes  that  have  occurred  in  it  since  it  was  formed. 
2.  What  shows  this  to  be  a  disused  quarry? 

Limestone  rock  is  made  from  animal  skeletons,  such  as 
shells  and  coral.  The  animals  get  carbonate  of  lime  —  of 
which  the  skeleton  is  composed  —  from  the  waters  of  the 
ocean  where  it  is  dissolved.  When  the  animals  die,  their 
skeletons  are  ground  up  by  the  action  of  the  waves.  The 
white  sand  and  mud  so  formed  are  very  fine-grained,  and 
when  consolidated  make  limestone.  Sometimes  the  lime- 


182     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

stone  is  colored  gray  or  streaked  with  black  from  the  carbon 
in  decayed  seaweed  and  animal  bodies.  The  chalk  cliffs 
of  Dover,  England,  are  a  kind  of  limestone  made  from 
shells  so  minute  that  they  need  no  grinding  to  form  a  fine- 
grained rock.  Limestone  is  much  used  as  a  building-stone, 
especially  in  the  central  and  middle  western  states. 

204.  Metamorphic  Rocks.  —  Crystalline  rocks  which  were 
made  from  sedimentary  or  igneous  rocks  are  named  meta- 
morphic  rocks.     These  rocks  were  made  by  great  pressure  or 
heat  in  the  presence  of  moisture.     The  heat,  not  sufficient 
for  melting,  was  caused  by  friction  between  layers  of  rock 
when  they  were  bent  or  pushed  up  in  mountain  making. 

Metamorphic  means  "  changed  in  structure."  Fragmental 
limestone  changes  to  crystalline  marble,  soft  shale  becomes 
slate,  and  sandstone  becomes  schist. 

Two  important  classes  of  metamorphic  rocks  are  gneisses 
and  schists:  gneisses  oftenest  produced  by  metamorphism 
of  granite,  and  schists  by  metamorphism  of  sandstone  and 
shale.  Gneisses  and  schists  contain  the  same  minerals  as 
granite,  but  in  different  proportions.  Gneisses,  containing 
a  large  proportion  of  feldspar,  split  into  thick  layers; 
schists,  containing  more  mica,  split  into  thinner  layers. 
Mica  schist  often  contains  crystals  of  the  mineral  garnet, 
which  is  used  as  a  gem. 

Some  of  the  flagstones  used  in  the  eastern  states  are  of 
local  schists,  but  the  better  flagstones  are  of  a  clayey  sand- 
stone from  New  York.  Curbstones  in  many  cities  are  cut 
from  gneiss.  Much  so-called  "granite"  is  really  gneiss. 

205.  Folded  Rocks. —  Metamorphic  rocks  in  hills  and 
mountains  are  often  composed  of  layers;  in  this  respject  they 
resemble  the  sedimentary  rocks  from  which  they  were  evi- 
dently made.     They  are  not  in  the   original   position  of 
such  rocks,  but  are  tilted  at  various  angles.     This  change 
in  position  of  the  rocks  came  about  in  the  following  way. 
As  the  heated  interior  of  the  earth  cooled,  it  shrank;   and 


THE  CRUST  OF  THE  EARTH         183 

the  colder  crust,  not  being  able  to  fit  the  shrinking  interior, 
wrinkled  and  formed  what  we  call  mountains.  The  once 
horizontal  rocks  were  folded  up,  while  igneous  material  of 
the  interior  was  squeezed  up  into  these  folds. 

206.  Dikes  and  Veins.  —  Sometimes,  in  this  process  of 
folding,  the  rocks  break,  forming  deep  cracks  or  fissures 
through  which  comes  melted  rock.  This  melted  rock  cools 
and  solidifies,  completely  filling  the  fissure  with  material 


FIG.  92.  —  DIKES;    SPANISH  PEAKS,  COLORADO 

The  wall-like  elevations  are  of  hard  lava  which  once  filled  fissures  in 
a  less  hard  rock.  The  latter  has  been  eroded  and  the  lava  has  been  left 
in  ridges  from  50  to  100  ft.  high.  What  shows  that  the  ridges  have  been 
somewhat  eroded? 

different  from  the  rock  on  either  side  of  it.  Such  a  forma- 
tion is  called  a  dike.  Its  width  may  be  a  few  inches  or 
hundreds  of  feet.  Its  resemblance  to  an  artificial  dike  is 
shown  when  it  is  harder  than  the  rock  near  it,  for  it  remains 
as  a  ridge  after  the  softer  rock  has  been  worn  away.  If  the 
dike  is  softer  or  full  of  cracks,  it  will  be  worn  away  faster 


184     FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 


than  the  rock  around  it,  but  the  formation  is  still  called  a 
dike.  Many  chasms  seen  in  the  rocks  at  the  seashore  are 
formed  by  the  wearing  out  of  a  dike. 

If  fissures  are  filled  with  minerals  left  by  evaporation  from 

solution,  the  material  fill- 
ing the  fissure  is  called  a 
vein.  Many  valuable 
ores  are  veins.  Gold  is 
oftenest  found  in  quartz 
veins. 

207.  The  Value  of 
Rocks  and  Minerals. 
—  The  crust  of  the  earth 
is  a  veritable  storehouse 
of  materials  from  which 
man  has  drawn  for  thou- 
sands of  years.  Build- 
ings still  standing  in 
ancient  cities,  as  Athens 
and  Rome,  show  that 
more  than  two  thousand 
years  ago  men  knew  how 
to  quarry  and  cut  stone. 
The  pyramids  of  Egypt 


FIG.  93.  —  A  CHASM  IN  A  SEASHORE 
CLIFF 


The  opening  between  the  rocks  was 
once  filled  with  igneous  rock.  There  were 
many  cracks  in  the  dike  caused  by  con- 
traction in  cooling.  1.  How  did  their 
presence  lead  to  the  removal  of  the  dike? 
2.  Will  the  chasm  widen  as  time  goes  by? 
Why? 


and  the  buried  temples 
and  palaces  of  Babylon 
are  even  older. 

The  modern  cities  of 
Europe  and  America  re- 
quire immense  quantities  of  stone,  which  is  shipped  from  re- 
gions where  it  is  accessible,  to  the  place  where  it  is  to  be  used. 
The  requirements  of  a  good  building-stone  are  firmness  of 
structure,  fine  grain,  and  resistance  to  water  and  changes  of 
temperature.  Sedimentary  rocks  and  rocks  which  were 
slowly  metamorphosed  best  fulfill  these  conditions. 


THE  CRUST  OF  THE  EARTH         185 

The  broad  valley  between  the  two  great  mountain  systems 
of  the  United  States  furnishes  sedimentary  rocks  but  no 
metamorphic  rock.  In  this  region  there  are  beds  of  lime- 
stone, hundreds  of  feet  thick.  In  many  places  the  cover- 
ing of  mantle  rock  is  thin  and  quarries  are  easily  opened. 
These  furnish  an  inexhaustible  supply  of  material  for  build- 
ings and  for  making  lime.  Lime  is  necessary  for  all  masonry 
and  concrete  work,  and  is  prepared  by  heating  limestone. 


i  i 

FIG.  94.  —  FOLDED  COAL-BEARING  ROCKS 

Dotted  line  =  surface  when  strata  were  folded.  a,  b  =  fragmental 
rock,  c  =  seam  of  coal,  d  =  present  surface.  /  =  faulted  fracture.  v  = 
an  eroded  valley.  1.  In  which  vertical  section  would  the  discovery  of  coal 
be  most  likely  to  occur?  Why?  2.  In  which  least  likely?  Why?  3.  How 
do  you  account  for  the  thicker  covering  at  c'f 

The  oldest  mountains  are  in  the  eastern  states  and  Cali- 
fornia. These  furnish  the  finest  metamorphic  rocks,  granite 
and  gneiss,  both  of  which  are  called  granite  commercially. 
The  granite  of  the  Rocky  Mountains  is  a  coarse  granite. 
The  lavas  of  the  Rocky  Mountains  are  used  for  trimming 
stones,  but  are  too  porous  for  other  use  in  regions  where 
the  atmosphere  is  humid. 

A  source  of  great  industrial  prosperity  in  this  country  is 
the  coal-supply.  Beds  of  coal  lie  between  beds  of  shale  and 
sandstone  in  large  areas  from  Nova  Scotia  to  Iowa  and  south 
to  Texas,  and  farther  west  on  the  slopes  of  the  Rocky  Moun- 
tains through  Mexico  and  Central  America.  Where  the 
strata  have  been  lifted  up  in  mountain  making,  the  coal  is 
fairly  accessible.  If  the  strata  have  been  very  much  com- 


186      FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 


pressed,  the  coal  is  hard  coal,  anthracite.  Through  the 
middle  and  western  states  the  coal  is  soft;  this  is  called 
bituminous  coal. 

Ores  of  iron,  silver,  gold,  and  lead  are  reckoned  of  inesti- 
mable value  to  a  country;  but  they  would  be  of  little  use 
without  coal,  which  is  used  as  a  fuel  in  separating  the  metal 
from  the  ore. 


COAL  FIELDS  IN 
THE  UNITED  STATES 


FIG.  $5.  —  COAL  FIELDS  IN  THE  UNITED  STATES 

1.  The  coal  fields  of  the  United  States  occupy  about  one  sixth  of  the 
area  of  the  country  (not  including  Alaska).  1.  In  which  half  of  the  coun- 
try is  the  greater  supply?  2.  In  how  many  states  is  coal  found?  3.  What 
is  the  importance  of  its  wide  distribution? 

Petroleum  is  found  in  many  regions  where  coal  is  inacces- 
sible. It  is  used  to  some  extent  as  fuel  in  locomotive  engines 
and  steamships. 

208.  Rock  Making  at  Present.  —  When  it  rains,  the 
water  flows  down  the  mountain  slopes,  making  rills  which 
combine  into  torrents;  these  join  and  make  larger  streams 
which  finally  reach  the  ocean.  This  running  water  is  at 
work  wearing  away  the  earth's  crust  and  making  valleys. 


THE  CRUST  OF  THE  EARTH 


187 


It  takes  away  soluble  minerals  in  solution,  and  carries  insol- 
uble fragments  with  its  current  to  the  sea.  There  the  frag- 
ments are  assorted  by  the  ocean  currents  and  finally  are  made 
into  sedimentary  rock.  (LABORATORY  MANUAL,  Exercise 
XIX.) 


FIG.  96.  —  CATHEDRAL  SPIRES  IN  THE  GARDEN  OF  THE  GODS, 
MANITOU,  COLORADO 

These  rocks  are  of  soft  red  sandstone.  The  highest  is  more  than  200  ft. 
high.  1.  In  what  position  are  the  layers  shown  here?  2.  What  was  their 
position  originally?  3.  What  connection  is  there  between  their  present 
position  and  the  rate  of  erosion? 

209.  The  Age  of  the  Earth.  —  Just  how  long  a  time  has 
been  required  to  bring  the  earth  to  its  present  condition  can- 
not be  known  exactly.  One  method  of  estimating  the  length 
of  time  is  by  calculation  of  the  average  rate  of  deposit  in 
river  deltas  whose  extent,  a  few  hundred  years  ago,  is 
known.  The  time  required  for  the  folding  into  mountains 
and  the  wearing  down  which  have  followed  in  some  particular 


188      FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 


region  must  be  ascer- 
tained by  knowledge  of 
the  rock  material  and 
the  agencies  at  work. 
The  Appalachian  Moun- 
tain system,  about  one 
hundred  miles  wide,  was 
formed  by  the  folding  of 
strata  of  f  ragmental  rock 
many  thousands  of  feet 
thick.  The  accumula- 
tion of  this  material 
under  the  water  is  esti- 
mated to  have  taken  at 
least  thirty-six  millions 
of  years.  Since  that 
was  done,  it  is  thought 
that  one  third  as  much 
time  has  elapsed.  Scien- 
tists conclude,  from  this 
estimate  alone,  that  the 
earth  must  be  many 
millions  of  years  old. 

Another  method  of 
judging  the  age  of  the 
earth  is  by  the  study  of 
fossils.  A  fossil  is  the 
remains  or  impression  of 
a  plant  or  animal  that 
was  buried  in  mud  or 
sand.  The  mud  or  sand 
afterward  became  rock 
and  thus  preserved  the 
hard  parts  of  the  body. 
The  soft  parts  decomposed  and  passed  off  as  gases  or  liq- 


FIG.  97.  —  FOSSIL  FORE  LIMB  OF  AN 
ANCIENT  REPTILE 

A  "fossil  hunter"  has  been  putting 
plaster  of  Paris  around  the  bones  and  in 
the  cracks  of  this  valuable  specimen  so  that 
it  can  be  safely  shipped  to  some  museum. 
1.  Compare  the  size  of  the  man's  hand  and 
the  foot.  2.  Compare  the  length  of  his 
arm  from  wrist  to  shoulder  with  the  fossil 
bones  between  the  foot  and  the  upper  end. 


THE  CRUST  OF  THE  EARTH  189 

uids,  but  they  left  imprints  from  which  the  character  of 
the  organism  can  be  determined.  Fossil  leaves  are  often 
found  on  layers  of  slate  in  beds  of  coal. 

Only  fossils  of  the  simplest  animals  and  plants  are  found 
in  the  lower,  older  rocks,  while  fossils  of  more  complex  ani- 
mals and  plants  appear  in  the  later  rocks.  The  study  of  life 
has  shown  some  of  the  changes  that  have  occurred  since  few 
and  simple  forms  of  plants  and  animals  began  to  live.  Long 
ages  must  have  elapsed  during  the  period  when  the  later, 
more  complex  forms  of  life  were  developing  from  the  simple 

forms. 

EXERCISES 

1.  What  kinds  of  matter  form  the  sediment  of  a  river?     Where  does 
it  come  from? 

2.  WThy  are  layers  of  shale  and  sandstone  found  with  coal  beds? 

3.  What  does  conglomerate  rock  tell  of  its  origin?     Why? 

4.  Why  does  the  folding  of  layers  of  rock  produce  great  heat? 

5.  What  changes  in  rock  does  the  heat  of  folding  cause? 

6.  (a)  Name  the  metamorphic  rocks  made  from  sandstone  and  shale. 
(6)  From  limestone. 

7.  Give  a  reason  why  more  coal  is  mined  in  Pennsylvania  than  in 
Indiana. 

8.  Iron  ore  from  the  vicinity  of  Lake  Superior  is  sent  to  Pennsylva- 
nia for  reduction.     Give  a  reason  why  it  is  sent  so  far  for  reduction. 

9.  Name  three  crystalline  rocks  consisting  of  the  same  minerals. 


CHAPTER  XVI 
CONTINENTS;    OCEANS 

210.  The  Relation  of  Land  and  Water.— If  we  could 
view  the  earth  from  a  great  distance,  we  should  see  vast 
stretches  of  level  water  broken  by  smaller  areas  of  uneven 
land.  The  water  is  all  one  body,  though  separated  into 
somewhat  distinct  parts  called  by  different  names.  The 
land  masses,  or  continents,  are  gathered  into  two  groups 
which  almost  meet  around  the  north  pole.  Two  thirds  of 
all  the  land  is  in  the  northern  half  of  the  globe.  The 
continents  are  like  the  tops  of  great  elevated  blocks  of  the 
earth's  crust.  Some  islands  are  parts  of  the  same  block  as 
the  neighboring  continent,  but  many  are  the  summits  of 
ocean  mountains  and  volcanoes. 

To  the  east  of  the  United  States,  the  continental  block 
extends  far  into  the  Atlantic  Ocean.  For  a  great  many  miles 
from  the  coast  the  water  is  shallow;  that  is,  it  is  six  hun- 
dred feet  deep  or  less.  It  then  suddenly  becomes  several 
thousand  feet  deep.  The  place  where  the  water  deepens 
is  the  eastern  edge  of  the  continental  block.  The  portion 
of  this  block  covered  with  shallow  water  is  the  continental 
shelf.  Newfoundland,  Cape  Breton  Island,  Martha's  Vine- 
yard, and  Nantucket  are  elevations  in  the  continental  shelf. 

Sand  and  mud  brought  from  the  land  are  all  the  time 
being  deposited  upon  the  continental  shelf.  As  the  sedi- 
ment collects,  it  adds  little  by  little  to  the  extent  of  the 
land,  just  as  the  rock  waste  brought  by  a  river  sometimes 
forms  a  great  delta  at  the  mouth.  A  slight  elevation  of 
the  continental  shelf  may  bring  above  the  surface  of  the 
water  many  acres  of  low  barren  plain  and  thus  extend  the 

190 


CONTINENTS;    OCEANS 


191 


border  of  the  continent.  The  now  fertile  Coastal  Plain  of 
the  middle  and  south  Atlantic  states  was  added  to  the 
continent  by  elevation  of  the  continental  shelf. 

211.  The  Story  of  the  Continents  Told  by  the  Rocks.  - 
We  have  seen  how  limestone  rock  was  formed  at  the  bottom 
of  the  ocean.  When  beds  of  limestone  are  found  to-day 
in  the  interior  of  a  continent,  as  they  are  in  Indiana,  Ken- 
tucky, and  neighboring  states,  it  shows  that  there  was  once 
a  shallow  sea  in  that  region.  If  the  limestone  is  bordered 
on  some  sides  by  beds  of  sandstone  and  shale,  it  is  evident 


Plate 


Mts. 


Plateau 


Plain 


Continental  Shelf 


Deep  Ocean 


FIG.  98.  —  THE  CONTINENTAL  BLOCK 


The  dotted  horizontal  line  represents  the  level  of  the  sea;  the  dotted 
vertical  line  represents  the  eastern  limit  of  a  continental  block.  1.  To  what 
point  does  the  continent  extend?  2.  What  change  of  elevation  would  in- 
crease its  area? 

that  the  limestone  was  formed  in  a  shallow  sea  which 
became  unfit  for  corals  and  such  water  animals  because 
of  the  wash  of  mud  from  the  land.  Corals  live  only  in 
clear,  warm,  and  shallow  waters. 

Layers  of  limestone  are  sometimes  succeeded  by  layers  of 
sandstone  and  shale.  This  shows  that  corals  and  shell 
animals  were  once  abundant  there;  but  as  conditions 
changed,  cooler  water  or  muddy  water  destroyed  the  life 
and  covered  the  remains  with  deposits  of  sand  or  mud. 

Ripple  marks  in  the  rock  show  where  the  water  was  very 
shallow  so  that  sand  and  mud  were  disturbed  by  wavelets. 
Imprints  made  by  falling  raindrops  prove  that  mud  was 


192      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

out  of  water  (perhaps  at  low  tide)  and  partly  dry  when  the 
drops  fell.  The  mud  must  later  have  been  slowly  covered 
and  more  mud  must  have  been  deposited  to  fill  the  imprints 
of  the  drops.  Such  relics  are  usually  found  in  very  thin 
layers  of  shale. 

By  such  observations,  some  of  the  past  history  of  a  con- 
tinent is  learned.     It  has  not  always  been  dry  land.     Wher- 


FIG.  99.  —  Low  TIDE  ON  A  CORAL  REEF 

The  coral  polyps  whose  skeletons  have  made  these  stone-like  masses, 
cannot  live  many  hours  out  of  water.  The  living  polyp  is  always  on  the 
surface  of  a  mass  representing  many  generations  of  ancestors.  1.  Which 
varieties  of  coral  would  resist  the  action  of  heavy  waves  longer,  the  branch- 
ing skeletons  (stag-horn  coral)  or  massive  coral  like  this?  2.  Is  this  scene, 
then,  probably  on  the  shore  of  an  ocean  or  an  interior  sea? 

ever  there  is  sedimentary  rock,  at  some  past  time  there 
has  been  water  to  deposit  sediment.  Fossils  tell  us  whether 
it  was  salt  or  fresh  water. 

212.  Changes  in  the  Size  of  Continents.  —  Study  has 
shown  also  that  the  continents  have  not  maintained  a 
steady  growth  in  size  by  increase  around  the  borders.  In 


CONTINENTS;    OCEANS 


193 


some  period  a  region  which  had  been  dry  land  was  sub- 
merged; then  later  it  was  again  elevated.  Some  continents 
have  lost  by  slight  subsidences  along  their  borders.  After 
hundreds  of  years  such  changes  have  brought  the  shore  line 
farther  inland  than  it  was  at  a  former  time  in  history. 

A  curious  example  of  successive  falling  and  rising  of  the 
borders  of  a  continent  is  found  at  Pozzuoli,  Italy.  A  temple 
built  near  the  sea  long 
before  the  Christian  era 
was  afterward  partly 
submerged  as  the  land 
sank.  There  is  no 
written  history  of  this 
event  and  none  is 
needed,  for  the  story 
is  told  on  the  stone 
pillars  of  the  temple. 
Upon  the  stone  many 
feet  above  the  level  of 
the  sea,  which  is  now 
quite  distant  from  the 
temple,  are  marks  made 
by  sea  shells  that  had 
grown  upon  the  pillars. 
They  were  as  securely 
fastened  there  as  barna- 
cles are  on  rocks  of 

the      shore      to-day,     raindrops  on  half  dried  mud.     It  also  tells 

These  shells  were  below    tha*  an  animal  with  a  foot  resembling  a 

bird  s  walked  over  the  mud. 

water  when   they  were 

parts   of   living  animals;    therefore   their  present   position 

shows  the  re-elevation  of  the  coast. 

An  evidence  of  continued  wearing  away  by  waves  is  seen 
in  the  diminishing  size  of  the  island  of  Helgoland  in  the 
North  Sea.  In  the  year  800  it  had  a  circumference  of  one 


FIG.  100.  — .FOSSIL  RAINDROP 
IMPRESSIONS 

This  piece  of  shale  is  an  old  weather 
report.     It  tells  of  a  short  shower  of  heavy 


FIG.  101.  —  RUINS  AT  POZZUOLI,  ITALY 

Study  of  these  ruins  has  shown  that:  1.  The  deposit  of  several  feet 
of  sediment  upon  the  floor  caused  the  building  to  be  abandoned.  2.  Later 
a  second  floor  was  laid  upon  the  sediment,  indicating  that  the  building  was 
used  again.  3.  Several  feet  of  deposit  were  removed  200  years  ago,  re- 
vealing the  remains  of  shells  grown  upon  the  pillars.  What  change  of 
level  is  indicated  (a)  by  the  covering  of  the  first  floor?  (6)  by  the  laying  of 
the  second?  (c)  by  the  presence  of  shells? 


CONTINENTS;    OCEANS  195 

hundred  and  twenty  miles.  In  1600  it  was  only  eight  miles 
in  circumference.  It  is  now  much  smaller,  being  a  little 
over  a  mile  long. 

213.  The  Location  of  Continents  in  Relation  to  History. 
Why   the   lands    of   the   earth    are   mainly    north    of   the 
equator,  and  why  there  are  land  projections  to  the  southward 
with  broad  expanses  of  ocean  between,  may  never  be  known. 
If  the  unoccupied  northern  lands  were  in  the  temperate 
latitudes  of  the  Pacific  Ocean,  their  climate,  the  history  of  the 
peoples  of  the  earth  and  their  occupations,  would  have  been 
vastly  different.     The  joining  of  two  continents  which  are 
now  separated,  or  the  separation  of  two  now  joined,  would 
have  resulted  in  great  differences  in  the  history  of  mankind. 
The  spread  of  peoples,  the  conquest  of  races,  and  the  devel- 
opment of  industries  would  all  have  been  different. 

214.  The  First  Oceans.  —  That  the  first  oceans  were 
not  pure  water  is  known  from  the  great  variety  of  salts 
dissolved  in  the  ocean.     These  salts  were  probably  formed 
by  the  chemical  action  of  acid  waters  on  the  metals  of  the 
rocks. 

215.  The  Composition  of  Sea  Water.  —  After  continents 
were  formed,  rivers  carried  material,  both  dissolved  and  in 
solid  form,  into  the  oceans.     To-day  every  soluble  mineral 
substance  known  in  the  solid  part  of  the  earth  is  to  be  found 
in  the  sea  water.     One  of  the  largest  constituents  of  sea 
water  is  common  salt,  which  forms  2J  per  cent  of  the  weight 
of  the  sea  water;  that  is,  from  1,000  grams  of  sea  water  25 
grams  of  salt  can  be  obtained.     The  sea  water  also  contains 
much  dissolved  air,  which  is  necessary  for  the  sea  animals 
that  breathe  by  gills.     Spray  tossed  from  the  waves  catches 
air  and  carries  it  back  to  the  sea. 

216.  The  Depth  of  the  Ocean.  —  The  average  depth  of 
the  ocean  is  two  and  one  half  miles.     The  greatest  depth  is 
about  twice  as  much,  while  along  the  shores  of  the  conti- 
nents a  child  may  sometimes  wade  safely  many  rods  from 


196     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

the  land.  The  ocean  bed  does  not  slope  uniformly  from 
the  edge  of  the  continent  to  the  deepest  water.  There  are 
ridges,  plateaus,  and  even  mountain  peaks  rising  from  the 
general  plain  of  the  ocean  bed. 

217.  Ocean  Temperatures.  —  Except  at  the  shores,  where 
the  water  is  somewhat  warmed  by  contact  with  rocks  and 
sand,  the  ocean  is  warmed  by  absorbing  heat  from  the  sun. 
The  heat  penetrates,  however,  only  a  few  feet  below  the 


FIG.  102.  —  TEMPERATURE  IN  AN  ENCLOSED  SEA  BASIN 

Water  enters  the  Gulf  of  Mexico  from  the  ocean  at  the  strait  of  Yuca- 
tan, where  the  water  is  about  1,000  fathoms  deep.  1.  What  is  the  ocean 
temperature  at  that  depth?  2.  What  is  the  greatest  depth  of  the  gulf? 

3.  What  is  the  temperature  of  the  coldest  water  that    enters    the  gulf? 

4.  What  is  the  temperature  at  the  bottom  of  the  gulf?     Why  is  it  not  so 
cold  as  that  at  the  bottom  of  the  ocean? 

surface.  The  temperature  of  the  surface  water  is  highest 
(ranging  from  80°  to  85°  F.)  in  the  tropics,  where  the  sun 
is  directly  overhead  somewhere  every  day  in  the  year.  At 
the  bottom,  the  temperature  of  the  ocean  the  world  over  is 
at  about  freezing  point. 

If  a  strait  connecting  a  partly  inclosed  body  of  water  with 
the  ocean  is  shallower  than  the  ocean,  only  the  warm  sur- 


CONTINENTS;    OCEANS  197 

face  water  passes  through  the  strait  into  the  smaller  body. 
As  a  consequence,  the  deepest  water  of  these  arms  of  the 
ocean  is  much  warmer  than  that  of  the  ocean  depths  out- 
side. The  Mediterranean  Sea  and  the  Gulf  of  Mexico  are 
both  much  warmer  than  the  ocean. 

218.  Currents.  —  Winds  blowing  constantly  in  one  direc- 
tion set  in  motion  currents  of  water,  and  so  in  the  ocean 
there  are  streams  of  water  flowing  through  the  quieter 
waters  on  either  side,  like  a  river  between  its  banks.  If 
these  currents  are  warm  waters  from  the  tropics,  they  carry 
and  distribute  heat  to  cooler  parts  of  the  world.  The  Japan 
Current  crosses  the  wide  Pacific  Ocean  toward  southern 
Alaska,  where  it  is  bent  southward,  and  after  moderating 
the  climate  of  the  states  on  the  Pacific  coast,  it  swings  again 
westward.  Logs  from  Oregon  forests  have  been  carried  by 
this  return  current  and  have  drifted  ashore  on  the  Hawaiian 
Islands. 

Cold  currents  from  the  arctic  regions  make  a  low  average 
temperature  from  Labrador  to  Massachusetts.  The  warm 
Gulf  Stream,  flowing  from  the  Gulf  of  Mexico  northeasterly, 
carries  heat  far  from  the  tropics  to  the  northern  countries 
of  Europe.  From  these  two  causes,  there  is  a  great  differ- 
ence between  the  average  temperature  of  the  northeastern 
part  of  the  United  States  and  that  of  the  same  latitudes 
in  Europe. 

Steamers  sailing  from  New  York  to  Europe  reach  the 
Gulf  Stream  about  the  third  day  out  and  passengers  then 
find  quite  superfluous  the  heavy  clothing  which  they  needed 
at  first.  The  air  over  the  warm  water  is  very  humid,  and 
when  icebergs  drift  into  or  near  the  Gulf  Stream,  dense 
fogs  result  from  the  condensation  of  the  vapor  carried  by 
the  warm  air.  When  the  warm  current  reaches  Great 
Britain,  the  westerly  winds  distribute  the  heat  and  mois- 
ture to  Ireland  and  Scotland  and  in  some  degree  to  England. 
These  lands  have  not  the  parched,  brown  look  of  much 


198     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

of  the  United  States  in  late  summer,  and  the  climate  is  much 
warmer  than  that  of  northern  Canada,  which  is  in  the  same 
latitude.  Even  as  far  north  as  60°  in  Norway,  cherries, 
strawberries,  and  some  vegetables  ripen,  while  in  northern 
Labrador  nothing  but  the  hardiest  plants  grow.  There  is 
as  little  trouble  from  floating  ice  in  the  harbor  of  the  most 


FIG.  103.  —  ST.  MARTIN'S  HEAD,  QUACO,  BAY  OF  FUNDY 

1.  Give  two  reasons  for  thinking  this  "head"  is  not  a  boulder  resting 
against  a  cliff.  2.  This  is  a  low  tide  scene;  high  tide  at  this  point  may 
be  30  ft.  higher.  Using  the  height  of  the  man  as  a  measure,  indicate  on  the 
"head"  the  place  which  high  tide  would  reach?  How  do  you  know  that  the 
water  at  high  tide  does  not  cover  the  rock? 

northern,  Norwegian  port  as  in  New  York  harbor,  which  is 
over  two  thousand  miles  farther  south. 

219.  Tides.  —  Besides  the  ceaseless  swinging  of  the  sur- 
face water  in  waves  and  the  onward  motion  of  the  currents, 
there  is  a  regular  rise  and  fall  of  the  water  along  all  shores. 


CONTINENTS;    OCEANS  199 

This  regular  movement  of  the  ocean  surface  is  known  as 
the  tide.  If  the  shore  is  steep  and  precipitous  like  a  wall, 
the  water  literally  rises  and  falls  vertically,  sometimes  several 
feet.  Where  the  shore  is  gently  sloping,  with  the  rising  of 
the  tide  the  water  moves  farther  inland,  covering  a  wide 
beach,  which  is  again  uncovered  as  the  tide  falls.  The 
water  mark  upon  a  stake  driven  vertically  into  the  sand 
at  the  low-tide  line  will  show  to  what  vertical  height  the 
water  rises  at  high  tide.  There  is  an  interval  of  a  little 
more  than  six  hours  between  low  tide  and  high  tide. 

It  is  known  that  this  piling  up  of  the  water  is  due  to  the 
attraction  which  the  sun  and  the  moon  have  for  the  part  of 
the  earth  directly  beneath  them.  The  moon,  because  of 
its  nearness,  has  a  stronger  attraction  than  the  sun.  The 
water,  which  is  the  movable  part  of  the  earth,  is  actually 
lifted  toward  the  moon,  making  a  huge  wave  which  follows 
on  across  the  ocean  after  the  moon. 

Currents,  waves,  and  tide  have  all  had  a  share  in 
making  the  borders,  and  in  some  cases  the  interior,  of 
continents  what  they  are  now. 

220.  The  Life  of  the  Ocean.  —  The  ocean  has  always 
been  of  immense  value  to  man  as  a  source  of  food  supply, 
and  its  value  is  constantly  increasing.  Nor  is  its  value 
confined  to  the  population  living  close  to  its  shores.  Thou- 
sands of  tons  of  salmon,  sardines,  and 'lobsters  are  annually 
canned  and  distributed  to  places  far  from  the  ocean.  Cod, 
herring,  and  other  fish  are  smoked  or  preserved  by  salt. 
Newfoundland  and  Norway  send  supplies  to  warm  coun- 
tries where  fish  cannot  be  so  well  cured  on  account  of  the 
heat.  The  use  of  ice  and  rapid  transit  make  possible  the 
distribution  of  fresh  ocean  foods,  and  now  more  than  ever 
we  depend  upon  the  ocean  for  food. 

The  living  things  of  the  ocean  have  by  their  shells  and  other 
hard  parts  contributed  greatly  to  making  layers  of  rock, 
sometimes  thousands  of  feet  thick.  These  rocks  are  now 


200     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

parts  of  mountains,  high  plains,  or  the  shores  of  a  con- 
tinent. Sea  shells  have  been  found  imbedded  in  rocks  in 
the  high  Alps  of  Europe  hundreds  of  miles  away  from  the 
sea.  The  upper  Mississippi  basin  of  North  America  is 
underlaid  with  layers  of  coral-limestone  rock.  Ocean  water 
furnished  mineral  matter  for  the  food  of  sea  animals,  and 
the  skeletons  of  these  animals  helped  to  make  the  land.  The 
ocean,  then,  not  only  furnishes  food  for  man,  but  has  been 
the  origin  of  large  areas  of  land. 

221.  The  Dependence  of  Lands  upon  the  Ocean.  —  If 
there  were  no  oceans,  the  earth  would  be  nearly  useless  to 
man,  for  the  lands  would  be  deserts.     Water  from  the  sur- 
face of  the  ocean  is  constantly  evaporating  and  passing  into 
the  air.     Vapor-laden  winds  from  the  ocean  pass  over  the 
continents,  the  vapor  condenses,  and  rain  or  snow  falls.     As 
soon  as  rain  water  touches  the  earth,  its  journey  back  to 
the  ocean  begins;    and   as  it   creeps  slowly  through  the 
ground,  it    brings  dissolved    minerals  to  plants,   and    fills 
springs  and  lakes  to  provide  man  and  beast  with  drink. 
During  the  last  stage  of  its  return  journey  the  water,  now 
become  a  river,  furnishes  power  by  which  work  is  done  by 
machines,  or  by  which  electric  currents  are  furnished  for 
light  and  power. 

222.  Ocean  Travel.  —  Even  before  the  days  of  the  Vi- 
kings, men  ventured  far  from  land  over  the  seas  in  search  of 
food,  wealth,  and  new  countries.     In  the  last  four  hundred 
years,  as  a  result  of  these  ventures,  North  and  South  America 
and  Australia  have  been  peopled  by  Europeans,  and  great 
nations  have  become  established.     We  may  now  travel  com- 
fortably for  business,  pleasure,  or  study,  completely  around 
the  world,  over  oceans  which  once  confined  people  to  the 
continents  on  which  they  were  born.     Where  continents  ob- 
structed an  ocean  journey,  canals  have  been  made,  as  at 
Suez   and   Panama,   so   that    goods  may   now   be    carried 
without  change  from  Boston  to  Japan  by  the  western  as 


CONTINENTS;    OCEANS  201 

well  as  by  the  eastern  route.  The  long  and  often 
dangerous  voyage  around  either  the  Cape  of  Good  Hope 
or  Cape  Horn  is  a  thing  of  the  past. 

EXERCISES 

1.  What  is  the  width  in  degrees  of  longitude  of  all  lands  lying 
between  the  tropics? 

2.  What  is  the  width  of  ocean  lying  between  the  tropics? 

3.  How  does  the  extent  of  ocean  compare  with  that  of  land  in 
the  south  temperate  zone? 

In  answering  Nos.  4-7,  suppose  that  all  the  continents  were  20° 
farther  south  than  they  are. 

4.  What  countries  would  the  equator  then  cross? 

5.  Would  any  continent  extend  into  the  antarctic  zone? 

6.  Would  the  area  of  tropical  land  be  increased  or  diminished? 

7.  How  would  conditions  in  Alaska  be  changed? 

8.  What  countries  of  South  America  does  the  meridian  of  Boston 
cross? 

9.  In  what  direction  from  New  York  is  the  main  part  of  South 
America? 

10.  What  is  the  only  isolated  continent? 

11.  Why  is  the  Red  Sea  warmer  than  the  Indian  Ocean? 

12.  What  changes  of  level  are  shown  by  the  ruins  of  Pozzuoli? 
Show  how  these  changes  are  known. 

13.  To  what  level  can  sediment  be  deposited  in  ocean  water? 


CHAPTER  XVII 
MOUNTAINS;    MINING;   FORESTRY 

223.  Changes  in  Elevation  of  Lands.  —  Two  kinds  of 
changes  in  the  surface  of  the  earth  occur  from  time  to  time: 
elevation  or  rising,  and  subsidence  or  falling.     These  changes 
of  level  are  usually  due  to  the  contraction  and  consequent 
wrinkling  of  the  earth's  crust.     As  a  result  of  the  elevation, 
new  land  may  be  lifted  above  the  ocean  level,  or  a  portion 
of  a  continent  may  be  raised  a  few  feet  or  thousands  of 
feet,   or    a  great  mountain    system   may  be   made.      The 
subsidence  may  reduce  the  area  by  bringing  portions  of  a 
continent  below  sea  level,  or  it  may  make  valleys  between 
elevations. 

Another  change  of  level  called  degradation,  or  lowering,  is 
going  on  all  the  time  wherever  high  land  is  exposed  to  the 
physical  and  chemical  changes  caused  by  air  and  water. 
The  general  name  of  this  work  is  erosion,  which  means 
"  wearing  away."  The  chief  agents  of  erosion  are  gravity, 
running  water,  moving  ice,  and  wind.  In  the  formation  of 
mountains,  erosion  plays  almost  as  important  a  part  as 
elevation. 

224.  Mountain    Making.  —  Mountains    are    formed    in 
three  ways:   by  the  erosion  of  high  lands;   by  the  breaking 
and  lifting  of  portions  of  rock  strata  as  a  result  of  unequal 
pressures  from  below;    and  by  the  folding  of  strata  over 
large  areas. 

225.  Mountains  of  Erosion.  —  Some  elevated  lands  are 
composed  of  horizontal  strata  which  have  been  lifted  so 
gently  from  their  position  beneath  the  water  that  the  strata 
have  scarcely  been  disturbed.     Slight  inequalities  of  level 

202 


MOUNTAINS;    MINING;    FORESTRY  203 

have  directed  the  flow  of  surface  waters,  which  by  erosion 
have  made  great  changes.  Cracks  in  the  rocks  give  en- 
trance to  air  and  water,  and  thus  erosion  begins  before 
uplifting  ceases.  Some  minerals  in  the  rocks  are  more 
soluble  than  others  and  some  are  softer;  thus  the  rocks 
wear  unequally.  The  result  is  a  group  of  peaks  or  ridges 
of  resistant  rock  with  ravines  and  valleys  of  different 
depths  between.  The  Catskills  and  the  mountains  within 
the  great  canyon  of  the  Colorado  in  Arizona  are  illustra- 
tions of  mountain  formation  by  erosion. 


FIG.  104.  —  FORMATION  OF  BLOCK  MOUNTAINS 
a,  6,  c,  d  =  four  rock  strata,     t  =  fragments  of  rock  called  talus. 

1.  Name  at  least  three  changes  which  have  occurred  in  these  strata 
since  they  were  made  at  the  bottom  of  the  sea.  2.  Account  for  the  presence 
of  the  talus.  3.  Under  what  conditions  might  a  lake  be  formed  at  I  ? 

226.  Block  Mountains.  —  Another  form  of  elevation  was 
caused  by  a  series  of  breaks  in  the  strata;    one  side  of  the 
break  was  pushed  up  or  the  other  fell.  .  The  result  is  a  suc- 
cession of  ridges  having  a  steep  slope  on  one  side  and  a 
gentle  slope  on  the  other.     These  are  called  block  mountains, 
because  at  the  time  of  the  uplift  the  strata  were  broken  into 
blocks.     The  mountains  of  the  Great  Basin  in  Utah  are  of 
this  origin. 

227.  Folded  Mountains.  —  A  third  form  of  mountain  was 
made  by  a  series  of  folds.     As  fragments  of  rock  worn  from 
the  land  were  brought  to  the  ocean  and  deposited  along  the 
continental  shelf,  they  were  consolidated  by  great  pressure, 
and  cemented  by  heated  waters  which  contained  dissolved 


204      FIRST  YEAR  COURSE   IN   GENERAL   SCIENCE 

quartz  or  limestone.  After  a  great  thickness  of  sediment 
had  been  deposited,  its  weight  weakened  the  rock  beneath. 
Then  contraction  and  the  pressure  of  the  ocean  block  against 
the  continental  block  wrinkled  the  crust  and  thus  a  fold  was 
made  along  the  weakened  rock.  The  result  was  a  slowly 


FIG.  105.  —  FOLDED  ROCK  EXPOSED  IN  A  RAILROAD  CUT, 
BERTON,  VIRGINIA 

This  is  not  a  part  of  a  mountain  now,  but  it  illustrates  the  first  form 
of  some  mountains.  1.  Is  this  igneous  or  sedimentary  rock?  How 
do  you  judge?  2.  The  camera  case  upon  the  rock  is  about  10  in.  long. 
Estimate  the  height  of  the  fold. 

uprising  fold,  or  sometimes  two  or  even  many  parallel  folds, 
as  in  the  'Appalachian  Mountain  system.  In  this  way  most 
of  the  great  mountain  systems  of  the  world  were  formed. 
When  they  were  uplifted,  they  were  near  the  borders  of  ah 
ocean  or  a  great  interior  sea!  They  have  since  been  worn 
down  so  much  that  all  appearance  of  folding  is  gone. 


MOUNTAINS;    MINING;    FORESTRY  205 

Fissures  extending  to  great  depth  were  made  when  the  rigid 
rock  beds  were  folded,  and  erosion  has  made  sharp  peaks  and 
narrow  clefts.  Such  mountains  are  called  young  mountains, 
as  if  there  had  not  been  time  enough  for  the  work  of  the 
atmosphere  to  smooth  the  rough  places,  round  the  sharp 
points,  and  carry  rock  fragments  down  the  sides  into  valleys 
where  they  might  be  borne  away  by  the  streams.  Some- 
times young  mountains  are  older  in  years  than  others  which 
appear  older,  because  hardness  of  the  rock  or  an  arid  climate 
has  delayed  the  work  of  change,  and  their  features  are  still 
rugged. 

228.  Degradation.  —  The  process  of  lowering  the  land 
has  been  occurring  ever  since  there  was  any  land  above  the 
level  of  the  sea.     The  work  of  the  atmosphere  tends  to  sepa- 
rate and  loosen  particles  at  the  surface  of  the  rock;  wind  and 
rain  carry  them  away.    The  result  of  this  work  is  denudation 
or  uncovering.     A  new  surface  is  then  exposed,  and  the 
work  continues,  all  the  time  lowering  the  average  level  of 
the  land.     But  while  degradation  is  taking  place,  the  land 
is  also  being  raised  slowly  by  the  wrinkling  of  the  solid 
crust  of  the  earth,  so. that  the  land  has  not  yet  been  brought 
down  to  the  level  of  the  ocean.     The  Appalachian  Moun- 
tains have  been  degraded  from  an  original  height  equal  to 
that  of  the  Rocky  Mountains.     The  Adirondacks  and  White 
Mountains  are  much  degraded  and  southern  New  England 
is  worn  down  almost  to  a  plain. 

229.  Veins.  —  The  folding  of  the  rocks  of  the  earth,  the 
breaking  which  accompanies  folding,  and  the  erosion  which 
follows,  have  been  the  means  of  bringing  valuable  minerals 
near  the  surface  on  mountain  sides.     Here  they  can  be  more 
easily  mined  than  if  they  lay  far  below  a  level  surface.     In 
the  process  of  formation,   the  fissures  in  the  rocks  were 
filled  with  minerals  in  solution  or  in  a  state  of  vapor. 
Crystals  were  deposited  from  these  solutions  on  the  sides 
of  the  fissures,  sometimes  completely  filling  them.     Such 


206     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

formations  are  called  veins.  They  may  contain  grains  of 
copper,  gold,  and  silver,  with  quartz  and  other  minerals. 
Sometimes  the  material  filling  the  vein  is  a  compound  of 
a  metal,  and  by  reduction  the  pure  metal  can  be  obtained. 
230.  Mining.  —  Metal-bearing  veins  occur  oftenest  in 
regions  of  disturbed  and  broken  rocks  which  are  found  in 
the  mountain  folds.  If  the  upper  rock  is  fractured  or  is 
soft,  it  becomes  worn  away  and  thus  a  vein  may  be  ex- 


FIG.  106.  —  INTERIOR  OF  A  MINE 

This  tunnel  enters  the  mountain  horizontally.  The  large  pipes  furnish 
compressed  air  for  running  machinery  for  drilling.  The  track  is  for  trans- 
portation of  materials  used  in  or  procured  from  the  mine.  1.  Mention 
material  of  both  kinds.  2.  Is  it  better  to  have  a  level  or  an  inclined  track? 
Why? 

posed  for  a  short  distance.  In  other  instances,  particles  of 
the  metal,  or  its  ore,  may  be  found  on  the  mountain  slope, 
but  the  end  of  the  vein  itself  may  be  as  completely  covered 
with  fallen  rock  waste  as  the  rest  of  the  mountain  side. 
Mines  are  frequently  opened  on  the  slopes  of  a  mountain, 
where  by  tunneling  horizontally  many  veins  may  be  crossed. 
The  most  promising  vein  is  then  followed  as  far  as  possible. 


MOUNTAINS;    MINING;    FORESTRY  207 

The  material  removed  in  tunneling  is  usually  taken  to  the 
mouth  of  the  tunnel,  and  there  dumped  on-  the  mountain 
side.  For  one  mine  in  operation,  there  are  many  heaps  of 
"dump"  which  show  where  unsuccessful  openings  have 
been  made. 


FIG.  107.  —  MARSHALL  PASS  ON  THE  DENVER  AND  Rio  GRANDE 
RAILROAD,  COLORADO 

This  is  one  of  the  highest  mountain  passes  (nearly  11,000  ft.)  in  the 
Rocky  Mountains.  1.  How  many  distinct  levels  of  track  are  seen  on 
this  side  of  the  pass?  2.  The  road  rises  about  3,000  ft.  in  25  miles.  What 
is  the  average  rise  per  mile? 

231.  The  Influence  of  Mountains.  —  The  location  of 
mountain  ranges  has  had  a  great  influence  upon  human  his- 
tory. In  olden  times  mountain  chains  were  such  obstructions 
to  travel  that  people  living  on  one  side  knew  nothing  of  those 
on  the  other.  The  Pyrenees,  the  Caucasus  Mountains,  the 
Andes,  and  the  Himalayas  are  examples  of  barriers  between 


208     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

countries.  In  the  settlement  of  North  America  it  took  two 
hundred  years  for  the  population  to  spread  beyond  even  the 
low  ridges  of  the  Appalachians.  With  the  advance  in  the 
science  of  engineering,  however,  and  the  application  of 
steam  power  in  locomotives,  railroads  have  been  built  over 
and  through  very  high  mountains. 

The  railroad  often  makes  long  detours  to  take  advantage 
of  a  valley  cutting  through  a  ridge,  or  winds  back  and  forth 
on  a  long  slope,  rising  at  each  turn  a  few  feet  above  the  last 
stretch  of  road.  In  climbing  a  mountain  a  few  thousand 
feet  in  elevation,  the  train  may  travel  many  times  the 
distance  across  the  range,  and  when  near  the  highest  part, 
passengers  may  look  down  upon  several  parallel  stretches  of 
road  over  which  they  have  passed. 

On  some  of  the  railroads  crossing  the  Rocky  Mountains 
in  the  United  States  tunnels  have  been  built  through  the 
highest  parts  of  the  mountains.  This  is  done  to  save  the 
time  that  would  be  required  to  haul  the  train  over  the  top, 
and  also  to  avoid  the  obstruction  of  the  track  by  snow 
avalanches.  The  greatest  tunnel  in  the  world  is  over 
twelve  miles  long,  through  the  Simplon  Mountain  between 
Switzerland  and  Italy. 

Mountains  are  famed  as  health  resorts  on  account  of  the 
purity  and  dryness  of  the  air,  and  for  summer  homes  because 
of  their  coolness  in  comparison  with  lower  regions.  The 
average  decrease  in  temperature  is  about  15°  F.  for  every 
5,000  feet  of  ascent. 

Mountains  act  as  barriers  to  the  spread  of  plants  and  ani- 
mals from  one  part  of  the  country  to  another.  Because  of 
cold  and  thin  soil,  trees  do  not  grow  above  certain  eleva- 
tions, called  the  timber  line.  If  the  summit  rises  beyond 
the  timber  line,  trees  cannot  spread  from  one  side  of  a  range 
to  the  other.  Above  the  timber  line  the  ground  is  covered 
with  short  grass  and  other  plants  which  do  not  require  long 
seasons.  As  a  rule,  the  flowers  of  mountain  plants  are  short 


MOUNTAINS;    MINING;    FORESTRY 


209 


stemmed  and  of  brilliant  color,  so  that  where  there  is  any 
soil,  the  ground  is  covered  with  a  variegated  carpet.  But 
these  plants  are,  like  trees,  adapted  to  their  surroundings 
and  are  not  found  beyond  certain  elevations.  The  summits 
of  high  mountains,  even  when  not  snow-covered,  are  often 
destitute  of  life. 

High  mountains  furnish  an  obstacle  to  wind  and  thus 
affect  the  climate.     Winds  blowing  from  the  ocean  are  moist 


FIG.  108.  —  TIMBER  LINE,  PIKE'S  PEAK 

How  do  you  account  for  the  fact  that  pine  trees  are  found  higher  up 
the  mountains  than  other  kinds  of  trees? 

winds.  As  they  meet  a  mountain  range,  the  air  rises;  it 
is  then  cooled  and  the  vapor  condenses.  Rain  or  snow  falls 
on  the  slope  toward  the  ocean,  and  a  dry  wind  passes  over. 
The  western  slopes  of  the  Sierra  Nevadas  are  well  watered; 
the  plains  to  the  east  are  deserts. 

232.    Forests  and  Forestry.  —  With  the  exception  of  a 
few  forest-covered  plains  in  the  northern  states,  the  moun- 


210     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

tains  bear  the  forests  of  our  country.  When  the  pioneers 
entered  a  new  region,  their  first  need  was  ground  suited 
for  agriculture.  Low  plains  along  the  rivers  were  ready  for 
plowing  and  planting;  but  in  the  East,  which  was  settled 
earliest,  the  plains  were  very  soon  occupied,  and  then  began 
the  felling  of  "  the  forest  primeval." 

People  are  now  beginning  to  realize  that  the  methods 


FIG.  109.  —  SCENE  FROM  A  WESTERN  FOREST 

1.  Observe  the  standing  timber  and  tell  what  it  promises  as  a  beginning 
for  a  new  forest.  2.  What  do  the  owners  gain  by  this  method  of  lumbering? 
3.  What  forest  "enemy"  have  they  introduced? 

properly  employed  by  the  pioneers  in  clearing  fields  for  agri- 
culture should  not  be  used  in  securing  wood  for  building, 
furniture,  or  fuel.  Much  waste  has  occurred  from  igno- 
rance of  right  methods  and  from  selfish  desire  for  the  pres- 
ent profit  only.  Young  trees  too  small  to  be  of  value  have 
been  cut  and  burned  to  clear  the  way  for  removing  larger 
trunks.  The  branches  cut  from  the  trees  have  been  left 


MOUNTAINS;    MINING;    FORESTRY 


211 


to  decay  slowly,  or  to  become  fuel  for  accidental  forest 
fires.  In  the  first  case,  new  growth  is  prevented;  in  the 
second,  much  young  timber  is  destroyed. 

Forestry  is  now  recognized  as  a  most  valuable  study.  Its 
object  is  to  discover  and  use  the  best  methods  of  managing 
forests. 


FIG.  110.  —  CONSERVATIVE  LUMBERING 

"Like  the  plant  of  a  successful  manufacturer,  a  forest  should  increase 
in  productiveness  and  value  year  by  year."  —  Practical  Forestry,  U.  S. 
Department  of  Agriculture.  1.  In  this  picture,  what  shows  that  the  owner 
agrees  with  the  Chief  Forester's  opinion  as  stated  above?  2.  What  is  the 
evidence  that  he  desires  to  get  the  greatest  net  money  return  from  the 
forest? 

233.  The  Division  of  Forestry.  —  The  United  States  has 
reserved  many  large  tracts  of  forest  land,  mainly  in  the 
Appalachian,  Rocky,  and  Sierra  Nevada  mountains.  The 
care  for  the  growth,  protection,  and  cutting  of  trees  in  these 
reservations  is  in  the  hands  of  the  Forest  Service.  This 


212     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

is  an  organized  body  of  trained  men  working  in  the  Forestry 
Division  of  the  Department  of  Agriculture.  Several  states 
also  and  many  individuals  have  reserved  forest  land  for  the 
purpose  of  scientific  management.  A  forest  can  be  made 
to  yield  a  steady  income  by  right  methods  of  cutting  trees 
of  a  proper  size  without  injury  to  smaller  ones,  by  careful 
removal  of  material  which  would  be  fuel  for  accidental  fires, 
and  by  replanting  areas  which  have  been  cleared. 

State  agricultural  schools  and  some  universities  have 
established  Schools  of  Forestry  to  fit  men  for  the  position 
of  foresters.  To  be  qualified  for  the  position,  a  man  must 
know,  among  other  things,  the  requirements  of  different 
kinds  of  trees  as  to  soil,  temperature,  light,  and  water;  the 
methods  by  which  each  kind  of  tree  distributes  its  seed; 
the  conditions  which  favor  the  growth  of  trees  from  the 
seed;  and  the  kinds  of  trees  which  grow  best  together. 

234.  Forest  Enemies.  —  The  enemies  of  the  forest,  which 
the  forester  must  recognize,   are  fire,   reckless  lumbering, 
sheep   grazing,   wind,    insects,   squirrels,    and   mice.     Each 
enemy  must  be  fought  by  the  best  means  available,  and 
these  the  forester  must  be  able  to  discover  and  use.     The 
methods  used  by  the  official  foresters  can  be  employed  with 
profit  by  every  owner  of  a  wood  lot. 

235.  Forests  and  Rainfall.  —  Much  has  been  said  about 
the  effects  of  forests  upon  rainfall,  climate,  and  floods.     It 
has  not  yet  been  proved  that  the  presence  of  forests  increases 
rainfall  or  changes  climate,  but  there  is  no  doubt  that  the 
removal  of  forests  from  large  areas  helps  to  cause  floods 
in  times  of  great  rainfall.     The  soil  of  a  living  forest  is  deep 
and   spongy,    and   prevents   the   rain   water   from   flowing 
immediately  into  streams;    and  the  surface  of  the  leaves 
upon  the  trees  and  undergrowth  holds  part  of  the  fallen 
rain.     Thus  the  streams  are  not  so  suddenly  filled  to  flood 
heights.     With  the  protecting  forest  removed,  the  ground 
becomes  hard;   and  when  the  soil  can  hold  no  water,  the 


FIG.  111.  —  A  FOREST  ENEMY;  RESULTS  OF  GRAZING 

Relate  the  story  told  by  these  pictures  of  a  forest  region  in  the  Pacific 
states  and  tell  of  its  probable  future. 


214     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

fallen  rain  must  run  off.  Excessive  rainfall  may  produce 
floods  even  in  forested  regions;  it  will  surely  do  so  in  de- 
forested regions. 

China  suffers  greatly  from  floods.  •  Its  forests  long  ago 
disappeared,  as  every  inch  of  land  was  needed  to  produce 
food  for  the  dense  population.  In  southern  California  floods 
from  the  deforested  San  Bernardino  Mountains  have  cov- 
ered fertile  lands  with  sand  and  gravel.  Later,  in  the  dry 
season,  when  water  is  needed  for  irrigation,  there  is  none 
in  the  beds  of  the  streams,  because  the  water  was  not  held 
back  by  the  trees  nor  absorbed  by  the  spongy  forest  floor. 

236.  The  National  Importance  of  Forests.  —  Young 
forests  are  sometimes  destroyed  by  fire  or  by  grazing.  Denu- 
dation follows,  and  the  soil,  from  which  a  new  forest  might 
have  grown,  is  carried  away  to  the  sea.  Correction  of  dam- 
age done  by  floods  has  already  cost  France  thirty-five 
million  dollars  and  the  task  is  still  unfinished.  These  floods 
resulted  from  the  destruction  of  forests  by  the  grazing  of 
sheep. 

The  prosperity  of  a  nation  depends  upon  its  ability  to 
provide  food,  water,  and  fuel  for  its  people.  Soil,  rivers, 
and  forests  are  necessary  to  this  provision.  There  is  no  more 
important  duty  of  the  government  than  to  guard  with  care 
and  to  develop  the  sources  of  its  prosperity. 

EXERCISES 

1.  How  early  in  the  history  of  a  mountain  or  a  continent  does 
degradation  begin? 

2.  Explain  what  is  meant  by  the  statement  that  "gravity  assists 
in  degradation." 

3.  Why  is  the  work  of  frost  more  rapid  in  mountains  than  in  plains? 

4.  What  is  the  appearance  of  young  mountains?     Why? 
6.  Why  is  the  air  purer  on  mountains  than  on  lowlands? 

6.  Tell  why  there  are  desert  regions  north  of  the  Himalayas. 

7.  How  long  must  the  track  of  a  railroad  be,  in  order  to  reach  an 
elevation  of  \\  miles  at  a  uniform  4%  grade  (a  rise  of  4  ft.  in  100  ft. 
of  track)? 


MOUNTAINS;    MINING;    FORESTRY  215 

8.  In  what  sort  of  places  are  most  of  the  gold  and  silver  mines 
located? 

9.  Explain  the  fact  that  the  gold  earliest  found  in  California  was 
in  the  sands  of  old  river  beds. 

10.  Why  is   there  a  short  season  for  growth  of  plants  on  high 
mountains? 

11.  Name  some  kind  of  injury  that  can  be  done  by  each  of  the 
forest  enemies  named  in  §  234. 


CHAPTER  XVIII 
TOPOGRAPHIC   MAPS 

237.  Map  Making.  —  By  the  topography  of  a  continent 
or  region  is  meant  the  description  of  its  physical  features  - 
mountains,  plains,  rivers.     There  are  several  ways  of  repre- 
senting differences  of  elevation  of  a  tract  of  country.     One  is 
the  method  of  relief  maps  by  which  the  region  is  pictured 
as  if  carved  from  a  solid  block.     Another  is  the  method  of 
hachures  or  shadings,  by  which  the  steeper  slopes  are  rep- 
resented by  heavier  shadings. 

A  third  method  is  that  of  contour  lines.  This  method 
is  now  used  in  all  topographic  maps  published  by  the  United 
States  government.  It  is  superior  to  the  other  methods 
because  it  shows  not  only  the  location  of  all  physical  fea- 
tures, but  also  the  exact  elevation  of  any  point  on  the  map. 

238.  Contour  Lines  and  Intervals.  —  A  contour  line  is  a 
line  on  which  every  point  represents  the  same  level.     Sup- 
pose we  stand  at  the  shore  of  the  ocean;  we  are  at  sea  level. 
Other  people  at  various  places  on  the  shore  are  at  the  same 
level.     A  line  representing  the  shore  is  the  contour  line  of 
zero  feet  above  sea  level.     One  person  might  climb  a  cliff 
a  few  feet  away  from  the  water  and  at  the  top  stand  twenty 
feet  above  the  sea  level,  while  another  might  walk  twenty 
rods  from  the  shore  before  he  rises  to  the  same  level  as 
the  top  of  the  cliff.     The  same  contour  line  would  pass 
through  the  points  where  these  two  people  stand,  but  it 
would  not  be  parallel  to  the  shore  line. 

The  space  between  the  two  contour  lines  would  represent 
the  horizontal  distance  from  the  shore  to  the  twenty-foot 
elevation.  The  contour  interval,  or  vertical  distance  between 


FIGS.  112,  113,  114.    CONTOUR,  RELIEF,  AND  HACHURE  MAPS 

1.  What  kind  of  region  is  represented  by  these  maps  ?  2.  Which  best 
shows  the  topography  ?  3.  Which  gives  the  most  exact  information  about 
the  elevations  ?  4.  Which  would  be  easiest  to  make  from  observation? 


218     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

the  lines,  would  be  twenty  feet.  The  zero-foot  line  and  the 
twenty-foot  line  would  come  nearest  together  at  the  steepest 
place. 

239.  Illustration  of  Contour  Lines  and  Intervals.  —  To 
illustrate  the  use  of  contour  lines  in  showing  the  form  of 
the  land,  suppose  that  a  cone  measuring  three  inches  high 
and  three  inches  across  the  base  is  cut  into  three  sections 
of  equal  thickness,  parallel  to  the  base.  A  long  pin  or  wire 
is  passed  through  the  center  of  the  three  sections.  The 
cone  is  placed  upon  paper  and  the  outline  of  its  base  is 
drawn.  It  is  a  circle.  The  lower  section  is  removed,  and 
the  remainder  of  the  cone  is  placed  upon  the  paper  with  the 
center  where  it  was  before.  Its  outline  is  another  circle 
smaller  than  the  first.  Continuing  the  work,  we  get  a  circle 
of  the  size  of  the  base  of  the  upper  section.  A  dot  at  the 
center  represents  the  top  of  the  cone.  Number  the  circles 
from  the  outer  one,  0,  1,  2. 

Make  a  diagram  of  the  front  view  (profile)  of  the  cone, 
showing  the  horizontal  sections.  On  the  side  of  the  profile 
number  the  base  0,  the  first  line  1,  and  the  second  line  2. 
Compare  the  cone  with  the  diagram.  The  base  of  the  cone 
is  0  inches  above  the  table.  The  circle  0  is  the  contour  line 
of  0  inches.  The  first  section  of  the  cone  is  1  inch  above 
the  table;  the  circle  1  is  the  contour  line  of  1  inch.  The 
contour  interval,  the  vertical  distance  between  them,  is  1 
inch.  Compare  other  points  on  the  cone  and  on  the  circles. 

Now  let  this  cone  represent  a  cone-shaped  volcano,  the 
contour  interval  of  which  is  500  feet  (that  is,  1  inch  on  the 
cone  represents  500  feet).  State  the  height  of  the  volcano 
above  the  level  0.  Name  the  contour  line  which  represents 
an  elevation  of  1,000  feet. 

The  length  of  the  line  0  represents  horizontal  distance,  and 
the  diameters  of  all  the  circles  represent  horizontal  dis- 
tances. The  base  of  the  cone  extends  three  inches  from 
east  to  west,  three  inches  from  north  to  south.  The  point  1 


TOPOGRAPHIC   MAPS 


219 


FIG.  115.    A  CONE  REPRESENTED  BY  CONTOUR  LINES 

The  upper  figure  is  a  profile  of  a  cone  cut  into  3  horizon- 
tal sections,  as  described  in  §  239.  The  lower  figure  represents 
by  its  outer  circle  the  base  of  the  cone;  the  second  circle 
(1)  represents  the  base  of  the  portion  of  the  cone  above  1,  the 
lower  section  being  removed.  1.  What  circle  would  represent 
the  journey  of  an  insect  around  the  base  of  the  cone?  2. 
Around  the  cone  at  the  point  2?  3.  If  the  insect  crawled  to 
the  summit,  where  would  it  be  in  respect  to  the  circular  figure? 


220     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

is  farther  west  than  the  point  0.  It  cuts  the  line  0  just  as 
far  to  the  west  of  0  as  the  point  1  on  the  circle  is  west  of 
the  point  0  on  the  circle. 

Land  forms  are  not  perfectly  symmetrical,  as  a  cone  or 
a  globe  is.  Let  the  dotted  outline  in  Fig.  115  represent  the 
real  profile  of  an  eroded  volcano.  The  contour  lines  of  this 
volcano  are  not  circles.  The  horizontal  distance  between 
them  is  not  uniform,  but  the  vertical  distance  between  them 
is  uniform.  (LABORATORY  MANUAL,  Exercise  XX.) 


FIG.  116.  —  CONTOUR  OF  AN  ISLAND 

240.  Reading  a  Contour  Map.  —  Fig.  1 16  is  a  contour  map 
of  an  island.     The  difference  of  elevation  represented  by 
successive  lines  is  50  feet.     The  island  is   5   miles    long. 
Determine  the  elevation  of  .the  highest  part.     Name  by 
direction  the  line  of  steepest  slope;    that  of  the  most  gentle 
decline.     Compute  the  average  descent  on  the  longest  slope, 
giving  the  number  of  feet  of  descent  to  the  mile. 

A  line  at  the  base  of  a  mountain  range  may  be  500  feet 
above  sea  level.  Calculating  from  that,  we  can  estimate 
the  altitude  of  the  summit  above  the  surrounding  country 
and  above  sea  level  by  counting  the  number  of  lines  above 
the  base  and  multiplying  by  the  number  of  feet  in  the  con- 
tour interval.  (See  Fig.  113.) 

241.  Valley  Contours. —  In  following  streams  on  a  topo- 
graphic map,  it  is  seen  that  the  contour  line  nearest  one 
bank  of  a  stream  is  of  the  same  elevation  as  the  line  nearest 


TOPOGRAPHIC   MAPS  221 

the  other  bank.  If  the  two  lines  are  followed  upstream,  it 
is  found  that  they  are  both  really  parts  of  a  single  line,  which 
crosses  the  stream  somewhere.  Farther  up  the  stream  the 
land  is  higher  than  this  first  line,  and  at  a  longer  or  shorter 
interval,  according  to  the  slope,  another  line  is  found  crossing 
the  stream.  The  contour  lines  consequently  bend  upstream. 
Where  there  is  no  stream,  a  similar  upward  bend  of  contours 
shows  the  presence  of  a.  valley,  as  is  indicated  in  Fig.  116. 

242.  Reservoirs. —  If  at  any  place  a  wall  is  built  across 
a  valley  with  its  top  at  the  elevation  of  the  contour  nearest 
to  the  stream,  the  water  flowing  down  the  valley  will  be 
stopped  by  the  wall.     When  the  water  has  reached  the  top 
of  the  wall,  it  will  have  overflowed  the  banks  of  the  river 
to  the  first  contour  level.     A  narrow  reservoir  will  be  formed, 
with  the  water  setting  back  upstream  to  the  place  where 
the  contour  line  crosses  the  stream.     If  the  dam  should  be 
built  between  the  second  contour  lines  from  the  river,  the 
reservoir  would  be  deeper  (as  much  deeper  as  the  number  of 
feet  in  the  contour  interval),  and  the  water  would  set  back 
to  the  crossing  of  the  second  contour. 

243.  Topographic   Maps   of   the    United   States.  — The 
United  States  Geological  Survey  has  undertaken  the  work 
of  making  topographic  maps  of  the  whole  country.     Each 
state  shares  the  expense  of  printing  the  maps  after  the 
government  survey  has  been  made.     The  scale  of  the  maps 
is  about  one  mile  to  the  inch.     If  all  the  maps  were  put 
together  to  make  a  map  of  the  United  States,  they  would 
measure  about  250  feet  from  east  to  west.     Each  sheet  of 
the  government  maps  represents  a  piece  of  country  thirteen 
miles  wide  (east  to  west)  and  seventeen  miles  long  (north  to 
south).     Contour  lines  are  in  brown  ink;  lines  representing 
man's  work,  such  as  boundary  lines,  roads,  and  railroads,  are 
in  black;   water  is    in  blue.     Houses    on    a    country  road 
are  shown  by  black  dots;   city  and  town  streets  are  solid 
black  lines.     (LABORATORY  MANUAL,  Exercise  XXI.) 


FIG.  117.    PART  OF  A  TOPOGRAPHIC  MAP 

Horizontal  scale  1  in.  =  1  mile.  Contour  interval  =  20  ft.  1.  What 
lines  on  this  map  tell  you  how  to  locate  the  region  in  the  United  States? 
2.  What  and  where  is  the  lowest  land  in  this  region?  3.  The  highest? 
4.  How  do  you  account  for  the  locations  of  the  railroad  lines?  5.  Does  the 
more*  southern  line  ascend  or  descend  after  leaving  the  Chicopee  River 
valley?  6.  Describe  as  to  habitation,  value  for  agriculture,  or  any  other 
occupation,  the  area  bounded  by  four  roads,  near  the  center  of  the  map. 


TOPOGRAPHIC  MAPS  223 

244.  Uses  of  Topographic  Maps. — Topographic  maps  are 
much  used  by  tourists  traveling  for  pleasure,  by  carriage  or 
automobile.  The  most  direct  roads  between  towns,  as  well 
as  the  more  circuitous  routes,  are  easily  traced.  Contour  lines 
show  the  ascent  or  descent  of  the  grade.  If  the  lines  cross- 
ing the  road  are  far  apart,  the  grade  is  gentle;  if  near  to- 
gether, a  steep  grade  is  indicated.  By  consulting  a  map,  the 
traveler  can  choose  at  a  fork  of  a  road  whether  he  will  take 
a  short,  steep  road  or  a  longer  one  with  a  more  gradual  rise; 
whether  he  will  drive  along  a  river  course  or  away  from  it. 

It  is  by  careful  study  of  elevations  as  shown  by  contour 
lines  that  sites  are  selected  for  reservoirs  for  irrigation, 
water  power,  or  city  water  supply.  The  first  condition  is, 
of  course,  a  permanent  and  sufficient  supply  of  water.  This 
is  generally  determined  from  the  number  of  square  miles 
included  in  the  basin  of  which  the  stream  is  the  outlet,  and 
the  average  rainfall  for  the  region. 

People  planning  for  a  summer  camp  can  select  the  site 
from  a  topographic  map  nearly  as  well  as  from  the  place 
itself.  The  positions  of  brooks  and  ponds,  hills  and  water- 
falls are  accurately  shown.  Distances  from  town  centers 
and  roads  are  correctly  indicated. 

In  planning  for  new  trolley  routes,  the  company  interested 
not  only  ascertains  the  best  grades  between  large  towns, 
but  sees  which  roads  would  go  through  regions  likely  to 
give  patronage,  and  where  the  line  could  leave  a  highway 
to  make  a  short  cut  through  the  woods  or  across  open 
country  with  the  least  loss  of  business.  All  these  things  can 
be  learned  from  a  study  of  the  maps. 

Maps  of  any  locality  whose  survey  is  completed  can  be 
obtained  at  Washington  for  a  small  sum.  The  survey  of 
many  of  the  eastern  states  is  already  finished;  but  in  the 
great  plain  and  prairie  regions,  only  the  populous  areas  or 
those  most  important  geologically  are  completed. 


224     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


EXERCISE   ON   A  SIMPLE   CONTOUR  MAP 


FIG.  118.    CONTOUR  MAP 

Contour  interval:   100  feet 

Horizontal  scale :   1  inch  =  1  mile 

1.  Fig.  118  is  a  contour  map  of  a  mountain  ridge  with  a  stream 
on  one  side.     What  is  the  height  of  the  summit  above  sea  level? 

2.  Trace  a  copy  of  this  map  upon  exercise  paper.     Rule  a  line 
from  a  point  representing  the  top  of  the  mountain  to  the  base  in  the 
direction  of  the  steepest  slope.     Label  the  line. 

3.  Rule  a  line  indicating  the  direction  of  the  gentlest  slope. 

4.  In  general,  how  do  you  distinguish  a  gentle  slope  from  a  steep 
slope? 

5.  In  particular,  how  do  you  select  the  gentlest  slope?    The  steepest 
slope? 

6.  What  is  the  length  of  the  river  shown  on  the  map? 

7.  What  is  its  average  fall  per  mile? 

8.  Calculate    the    actual    length    of    the   shortest   path  from   the 
summit  to  the  base  of  the  mountain.     (Put  down  your  calculations.) 


CHAPTER  XIX 
EARTHQUAKES;    VOLCANOES 

245.  Causes  of  Earthquakes.  —  In  the  process  of  moun- 
tain making,  the  thick,  rigid  layers  of  rock  bend  and  break 
here  and  there,  and  when  a  fracture  occurs,  there  is  a  mighty 
jarring  of  rocks,  sometimes  perceptible  for  many  miles.  The 
earthquake  motion  on 
the  surface  of  the  earth 
is  really  a  side  to  side 
movement,  as  is  shown 
by  the  swinging  of 
chandeliers  and  of  pic- 
tures upon  walls,  and 
even  by  the  swaying 
of  chimneys.  The  sen- 
sation which  people 
experience  is  one  of 
giddiness,  such  as  is  pro- 
duced by  unexpected 
swaying  of  the  body. 

It  is  the  surface  motion 

FIG.  119.  —  ONE  RESULT  OF  THE 
SAN  FRANCISCO  EARTHQUAKE 


that  is  called  an  earth- 
quake. 

The  fracture  below 
may  cause  the  broken 
rock  to  separate  and  the 
separation  may  extend 
upward  to  the  surface,  or 
the  fracture  may  make  the  broken  edges  slip  up  or  down. 
In  the  latter  case,  the  displacement  is  called  a  fault. 

225 


1.  If  this  crack  had  been  made  under 
a  building,  what  would  probably  have 
been  the  effect?  2.  Measure  the  widest 
part  of  the  crack  and  compare  it  with  the 
length  of  a  block.  3.  An  ordinary  paving 
block  of  this  form  is  about  10  in.  long; 
what  is  the  width  of  the  crack? 


226     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

Young  and  growing  mountains  are  likely  to  be  the  centers 
of  earthquake  disturbance.  By  means  of  delicate  instru- 
ments for  detecting  and  recording  the  direction  of  the 
movement,  scientists  can  locate  the  region  where  the  rocks 
parted,  sometimes  several  miles  below  the  surface. 

During  volcanic  eruptions,  earthquakes  are  caused  by  the 
sudden  pressure  of  expanding  steam,  which  has  the  effect 
of  a  blow  upon  the  rocks.  When  the  steam  finds  an  outlet, 
the  shaking  ceases. 

246.  Effects    of    Earthquakes.— The    vibrations    of    a 
severe  shock  are  felt  in  every  direction  for  long  distances 
from  the  center  of  disturbance.     But  earthquakes  make  very 
little  change  in  the  surface  of  the  earth.     They  may  cause 
a  landslide,  or   a  lifting  up  of  a  piece  of  ground,    or  an 
opening  like  a  ditch  varying  from  a  few  inches  to  some 
feet  in  width;    otherwise  they   make  little  change  except 
in  man's  handiwork.     It  is  the  suddenness  of  the  shock 
which  damages  buildings  and  thus  causes  loss  of  life. 

247.  Famous  Earthquakes.—  In  "  The  One  Hoss  Shay," 
Oliver  Wendell  Holmes  refers  to  a  disaster  in  Portugal  in 
1755: 

"  That  was  the  year  when  old  Lisbon  town 
Saw  the  earth  open  and  gulp  her  down. 

It  was  on  that  terrible  earthquake  day 

That  the  Deacon  finished  the  One  Hoss  Shay." 

In  1812  a  great  depression  of  the  surface  occurred  in  Mis- 
souri, and  the  most  violent  earthquake  known  to  the  United 
States  resulted.  About  seventy-five  years  later  there  was 
an  earthquake  which  was  most  severe  near  Charleston, 
South  Carolina.  In  one  minute  many  houses  were  entirely 
wrecked  and  thousands  of  chimneys  were  thrown  down. 
Outside  the  city,  a  rent  some  rods  in  length  was  made  in 
the  ground.  The  shaking  was  felt,  in  a  less  degree,  from 
Boston  to  Cuba.  These  are  the  only  serious  earthquakes 


EARTHQUAKES;    VOLCANOES  227 

which  have  been  felt  in  the  eastern  half  of  the  United  States 
since  its  occupation  by  Europeans. 

In  1906  a  severe  earthquake  occurred  in  California,  in 
and  about  San  Francisco.  It  was  caused  by  the  faulting 
of  rocks  along  the  line  of  a  break  which  had  been  made 
years  before.  Many  lives  were  lost  and  much  property  was 
destroyed.  Fire  followed  the  earthquake,  and  as  the  water- 
mains  had  been  broken  and  the  fire  department  was  without 


FIG.  120.  —  EFFECTS  OF  AN  EARTHQUAKE  AT  MESSINA 

1.  Which  would  have  more  elasticity,  a  wooden  building  or  a  stone 
building?  2.  Which  would  be  least  injured  by  a  swaying  motion,  a  one- 
story  building  or  a  higher  one?  3.  A  building  with  a  broad  or  a  narrow 
base?  4.  Give  directions  for  the  erection  of  an  earthquake-proof  structure. 
5.  Have  you  read  of  a  country  where  such  buildings  are  erected? 

water  to  fight  the  fire,  $500,000,000  worth  of  property  was 
destroyed  before  the  fire  was  conquered. 

Regions  in  which  earthquakes  are  of  most  frequent  occur- 
rence, for  example  the  Pacific  coast  region  from  California 
to  Chili,  are  near  young  mountain  chains.  Japan  and  Italy 
have  suffered  from  numerous  earthquakes,  some  of  which 
are  known  to  have  been  of  volcanic  origin.  But  the  two 


228     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

most  severe  ones  of  modern  times  were  undoubtedly  due 
to  faulting,  as  no  marked  volcanic  disturbance  occurred  at 
the  same  time. 

In  1908  two  large  cities  on  opposite  sides  of  the  Strait  of 
Messina  were  almost  totally  destroyed  by  violent  earth- 
quake shocks.  Seventy-five  thousand  people  were  killed 
and  as  many  more  were  injured  or  rendered  homeless. 
Practically  every  building  of  any  considerable  height  was 
wrecked.  The  center  of  the  disturbance  was  under  the  sea 
in  the  Strait  of  Messina.  An  earthquake  second  only  to 
that  of  Messina  occurred  early  in  1915  in  the  Italian  prov- 
ince of  Abruzzi  in  the  Apennine  Mountains.  There  are  no 
large  cities  in  this  region,  but  many  towns  and  villages 
were  completely  destroyed,  and  all  communication  by  wire 
and  rail  was  cut  off.  The  loss  of  life  was  between  twenty 
and  thirty  thousand.  The  tremors  were  felt  to  a  distance 
of  three  hundred  miles  and  some  of  the  monuments  and 
ancient  buildings  in  Rome  were  damaged. 

248.  Volcanoes.  —  Scattered  over  the  earth,  sometimes 
in  groups  but  often  singly,  there  are  cone-shaped  elevations 
called  volcanoes,  or  volcanic  mountains.  If  a  volcano  is 
active,  steam  is  seen  rising  above  its  summit;  fine  rock  dust, 
called  ash,  is  blown  in  clouds  from  the  opening  at  the  top; 
and  melted  rock,  or  lava,  pours  down  the  slope'.  At  the 
summit  of  many  volcanoes  there  is  a  bowl-shaped  depression 
called  the  crater,  which  is  sometimes  partly  filled  with  lava 
even  when  none  flows  over  the  edges. 

A  volcano  is  said  to  be  dormant  when  for  a  long  time 
there  has  been  no  sign  of  activity.  If  sufficient  time  has 
elapsed  for  the  crater  to  become  filled  with  rock  waste  or 
water,  and  the  sides  to  be  covered  with  soil  and  forested  or 
cultivated,  the  volcano  is  considered  extinct.  Mount  Shasta, 
an  extinct  or  dormant  volcano  of  California,  has  been  quiet 
so  long  that  glaciers  have  formed  upon  its  sides.  Mount 
Lassen,  another  California  volcano,  began  to  send  out 


EARTHQUAKES;    VOLCANOES 


229 


clouds  of  steam  and  ash  in  the  spring  of  1914.  It  had 
never  before  been  seen  in  eruption,  but  now  it  can  no  longer 
be  considered  even  dormant. 

249.  Famous  Eruptions.  —  Vesuvius,  near  Naples  in  Italy, 
had  been  so  long  dormant  that  when  a  great  eruption 
occurred  in  79  A.  D.,  the  people  living  near  by  were  utterly 


FIG.  121.  —  VESUVIUS  AS  SEEN  FROM  ACROSS  THE  BAY  OF  NAPLES 

From  this  position,  it  looks  as  if  there  were  two  peaks  to  Vesuvius. 
There  is,  in  fact,  only  one  peak.  The  elevation  to  the  left  is  a  part  of  the 
rim  of  an  old  crater  which  was  blown  away  at  the  eruption  in  A.  D.  79.  A 
column  of  steam  is  rising  almost  all  the  time  from  Vesuvius.  1.  Why  should 
it  often  look  red  at  night?  2.  Account  for  the  red  streaks  sometimes  seen 
at  night  on  the  slope  of  the  mountain. 

incredulous  that  harm  could  come  to  them.  Even  though 
black  clouds  of  ash  were  falling  upon  them  and  shocks  of 
earthquake  were  repeatedly  felt,  they  could  not  believe  that 
there  was  real  danger.  Two  cities,  Herculaneum  and 
Pompeii,  were  completely  buried  by  this  eruption.  The 


230     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

ash  and  condensed  steam,  falling  as  rain,  made  a  mud 
covering  which  after  some  time  hardened  into  stone.  The 
location  of  the  ancient  Pompeii  was  discovered  in  1748. 
Excavations  which  have  been  made  -since  that  time  show 
that  the  mud  crept  into  all  places,  even  into  ovens  and 
chests  in  the  houses.  Articles  and  bodies  buried  by  it  have 
been  preserved  in  form  by  the  mud  which  hardened  around 
them.  The  hardening  mud  formed  a  mould  having  exactly 
the  form  of  the  object  within,  and  after  a  time  the  object 
crumbled  to  dust.  The  remains  have  been  removed  and 
plaster  casts  have  been  made  in  the  moulds.  Jewel  boxes, 
loaves  of  bread,  and  a  watch  dog  chained  beside  a  door  are 
some  of  the  objects  which  have  been  reproduced  in  this 
way. 

In  1906  there  was  a  violent  eruption  of  Vesuvius  which 
destroyed  many  small  villages  on  the  slope.  Streams  of 
lava  overflowed  and  also  burst  through  the  sides  of  the 
crater,  burying  houses  and  fertile  fields. 

Sometimes  poisonous  and  very  hot  gases  pour  down  the 
slopes  of  a  volcano,  causing  death  to  plant  and  animal  life. 
Such  was  the  case  in  the  eruption  of  Mount  Pelee  in  the 
West  Indies  in  1902.  More  lives  were  lost  there  than  at 
Pompeii,  but  they  were  destroyed  by  superheated  steam 
and  other  hot  gases.  The  ruins  of  the  city  of  St.  Pierre, 
near  Mount  Pelee,  were  not  buried  as  Pompeii  was.  There 
were  no  survivors  to  rebuild  the  city,  as  San  Francisco  was 
rebuilt,  and  it  is  still  a  desolate  waste. 

250.  The  Cause  of  Volcanic  Eruptions. —  There  are  a 
few  volcanoes  which  have  been  made  since  history  began, 
and  descriptions  by  eye-witnesses  are  recorded.  From  an 
opening  in  the  ground,  or  sometimes  from  under  the  sea, 
rose  clouds  of  steam,  and  columns  of  ash  and  rock,  or  lava. 
The  solid  matter  fell  around  the  opening  and  built  up  a 
cone,  and  the  hardening  lava  added  to  its  extent.  Many  of 
the  cone-shaped  volcanoes  undoubtedly  began  in  this  way. 


EARTHQUAKES;  VOLCANOES         231 

Others  began  where  there  were  fissures  in  rocks  that  were 
rising  or  were  already  uplifted.  In  one  case  a  single  erup- 
tion began  and  ended  the  life  of  a  volcano  two  hundred 
feet  high,  south  of  Sicily.  The  cone  has  since  been 
swept  away  by  the  sea  and  nothing  but  a  ledge  of  rock 
remains. 

An  eruption  is  probably  caused,  in  most  cases,  by  the 
great  pressure  of  the  steam  formed  in  regions  where  water 
has  percolated  to  heated  rock  far  below  the  surface.  Since 
unconfined  steam  occupies  about  1,700  times  as  much  space 
as  the  water  from  which  it  is  made,  its  pressure  when  con- 
fined is  tremendous.  As  it  pushes  its  way  out,  it  often  forces 
out  solid  rock  above  it,  as  well  as  the  liquid  rock  which  is 
near  it.  Some  of  the  lava  rises  into  the  air  in  a  fine  spray, 
as  water  does  from  a  hose,  but  it  solidifies  in  the  air  and  falls 
as  a  fine  dust,  called  volcanic  ash. 

Before  an  eruption,  the  earth  is  often  violently  jarred  and 
shaken  by  the  expanding  steam,  and  the  resulting  earth- 
quake is  thus  a  warning  of  an  eruption.  The  whole  side 
of  the  volcano  is  sometimes  blown  away  by  an  especially 
explosive  eruption,  as  in  Krakatoa,  in  the  Straits  of  Sunda, 
near  Java,  in  1883. 

Volcanoes,  like  earthquakes,  are  more  numerous  in  young 
mountain  regions  than  in  old  ones,  because  while  the  folding 
of  the  rocks  is  going  on,  the  fractures  provide  openings  for 
the  release  of  the  melted  rock,  which  is  always  under  pres- 
sure below. 

251.  Lava  Sheets  and  Dikes. —  Volcanic  action  does  not 
always  produce  a  typical,  cone-shaped  volcano.  Sheets  of 
lava  may  flow  over  a  great  extent  of  country,  through  a 
fracture  one  hundred  or  more  miles  in  length.  Such  old 
lava  flows  are  found  in  states  west  of  the  Rocky  Moun- 
tains, where  they  cover  an  area  of  150,000  square  miles  in 
Idaho,  Washington,  and  Oregon. 

When  the  liquid  rock  cools  in  the  fissures,  it  closes  the 


232     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

opening.  If  the  rock  on  either  side  of  the  fracture  is  softer 
and  becomes  worn  down,  the  harder  rock  stands  like  a  ridge 
or  dike. 

EXERCISES  . 

1.  What  changes  in  the  surface  of  the  earth  are  sometimes  caused 
by  earthquakes? 

2.  Why  is  there  loss  of  life  by  earthquakes  when  there  is  no  per- 
manent effect  on  the  earth's  surface? 

3.  Use  the  terms  cause  and  effect  correctly  in  describing  a  connec- 
tion between  volcanoes  and  earthquakes. 

4.  What    are   the    earthquake    regions    of    North   America?     Of 
Europe? 

5.  What  is  the  volcanic  region  of  North  America?     Of  Europe? 

6.  Explain  any  relation  between  the  answers  to  Ex.  4  and  Ex.  5. 

7.  How  does  one  judge  whether  a  volcano  is  extinct  or  dormant? 

8.  What  changes  take  place  in  the  form  of  an  extinct  volcano? 

9.  How  long  have  we  had  any  history  of  California  and  Oregon, 
which  contain  our  only  volcanoes? 

10.  How  is  volcanic  ash  made? 

11.  Why  are  volcanoes  found  in  the  regions  of  growing  mountains? 

12.  Describe  a  volcanic  dike. 


CHAPTER  XX 
RIVERS    AND    THEIR   WORK 

252.  Temporary  Streams. —  In  places  where  the  surface 
is  bare  rock,  every  rainfall  sends  sheets  of  water  flowing 
over  the  slopes  and  streams  rushing  in  the  ravines.     The 
flow  ceases  when  the  rainfall  does.     Such  temporary  streams 
are  found  on  rocky  slopes  of  deforested  hillsides  and  in  gul- 
lies in  semi-arid  regions.     Travelers  crossing  barren  country 
are  sometimes  caught  by  a  flood  while  camping  in  a  seemingly 
desert  hollow.      It  is  important  in  the  study  of  rivers  to 
know  how  the  loose  covering  of  the  earth  was  made,  because 
that  covering  holds  the  rain  water  for  a  time  and  makes 
possible  the  beginning  of  permanent  streams. 

253.  Weathering. —  The  earliest  lands  were  of  rock  with 
no   covering   of   plants   and   with   no   animal   inhabitants. 
Animals  cannot  live  without  plants,  and  few  plants  grow 
upon  bare  rock.     But  the  rock  began  to  decay  almost  as 
soon  as  it  was  formed,  and  decayed  rock  is  the  beginning 
of  soil. 

Many  natural  forces  act  together  to  wear  away  the  sur- 
face of  rocks.  The  oxygen  and  carbon  dioxide  of  the  air,  in 
combination  with  water,  act  chemically  upon  some  minerals 
to  change  their  composition  and  cause  crumbling  and  decay. 
Water  enters  crevices  in  a  rock;  freezing  there,  it  expands 
about  one  tenth  of  its  volume  and  forces  the  rock  apart. 
The  sun's  heat  also  expands  the  surface  layer  and  loosens 
it  from  the  under  rock,  and  rain  and  wind  remove  the 
grains  which  afterward  accumulate  in  hollows.  The  wearing 
away  of  rock  in  these  ways  is  called  weathering. 

233 


234     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

In  the  course  of  time  the  earth  became  covered  with  an 
accumulation  of  rock  fragments;  this  covering  is  called 
mantle  rock.  By  the  process  of  decay,  a  thin  covering 
capable  of  supporting  plant  life  was  formed. 


FIG.  122.  —  WEATHERED  ROCK 

1.  What  evidence  do  you  see  of  the  work  of  air,  water,  and  changes  of 
temperature  on  this  rock?  2.  How  do  you  account  for  the  fine  material 
around  the  base? 

254.  Soil.  —  Decayed  rock  material  containing  animal  or 
vegetable  matter  is  called  soil.  Some  forms  of  plants  can 
secure  all  the  material  they  need  to  make  food  from  air, 
water,  and  rock  waste,  especially  if  the  rock  waste  is  of 
volcanic  origin.  Such  plants  would  be  the  first'  to  flourish 
on  new  land;  their  remains  would  contribute  to  soil  and  their 
roots  would  assist  in  the  process  of  weathering.  Earthworms 
and  burrowing  animals  also  are  agents  of  weathering  and 
assist  in  making  soil.  Even  now,  after  millions  of  years, 


RIVERS  AND  THEIR  WORK  235 

much  of  the  earth's  surface  has  only  a  few  inches  of  soil, 
although  in  some  old  valleys  the  soil  is  many  feet  thick. 

255.     The  Formation  of  Rivers. —  The  soil  filled  with  roots 
of  living  plants  and  the  broken  rock  beneath  it  retain  for 


FIG.  123.  —  ERODED  SOIL 

This  is  a  place  where  a  road  is  being  made.  Streams  caused  by  a  heavy 
rain  have  cut  deeply  into  soft  earth.  1.  What  becomes  of  material  taken 
out  by  rain  water?  2.  Why  does  not  this  happen  on  all  slopes  every  time  it 
rains?  3.  What  reason  can  you  give  for  the  fact  that  hillsides  are  not  often 
planted  for  crops  that  require  cultivation?  , 

a  short  time  some  of  the  water  which  falls  upon  the  ground. 
Gravity  makes  the  water  sink  slowly  through  cracks  and 
porous  rock  until  it  reaches  some  less  porous  stratum.  If 
this  stratum  slants  downward,  the  water  follows  the  rock 
until  it  comes  to  the  surface  lower  down  the  mountain. 
There  is  then  a  constant  discharge  of  water  which,  running 
as  a  little  brook  in  a  valley,  may  be  the  beginning  of  a 
river.  Other  brooks  join  it;  springs  from  the  valley  slopes 
feed  it  here  and  there;  rivers  from  side  valleys  bring  water 


236      FIRST  YEAR  COURSE -IN  GENERAL  SCIENCE 

from  othe"r  hills;  and  a  mighty  river  carries  it  all  to  the 
sea. 

256.  The  Load  of  Rivers.-—  There  is  much  besides  water 
that  is  being  carried  to  the  sea  by  the -rivers.  The  load  of  a 
river  consists  of  dissolved  mineral  matter  and  rock  waste 
in  the  form  of  mud  and  sand.  All  this  has  been  gathered 
from  every  part  of  the  land  whence  water  has  flowed  into 


FIG.  124.  —  SURFACE  SPRING 

i  represents  impervious  rock;  p,  h,  porous  rock;  c,  loose  earth;  s,  a  hill- 
side spring;  r,  a  river  bed.  1.  What  is  the  source  of  water  flowing  out  at 
sf  2.  Does  it  come  out  with  great  pressure?  Why?  3.  If  a  wall  were 
built  around  the  spring,  how  deep  could  the  water  be  in  the  basin,  as  judged 
by  this  diagram?  4.  Describe  the  stream  that  would  flow  from  s  to  r. 


the  river.  The  Mississippi  River,  which  carries  a  greater  load 
than  any  other  river  in  the  United  States,  gathers  it  from  the 
mountains  of  Montana,  the  forests  of  Minnesota,  the  farms 
of  Kentucky,  and  other  lands  along  its  course. 

It  is  hard  to  realize  how  much  solid  material  a  river  carries. 
It  deposits  its  load  on  the  banks,  in  the  bed  of  the  stream,  and 
at  the  mouth.  A  swift  current  carries  much  material,  coarse 
and  fine,  and  deposits  none.  A  slower  current  drops  coarse 
material  and  carries  only  the  finer.  When  a  river  enters  a 
lake  or  the  sea  and  its  current  is  checked,  it  usually  drops 
the  last  of  its  load.  Whether  the  material  settles  here  or 
is  carried  farther  and  distributed  by  currents  and  waves  of 
the  sea,  depends  upon  the  form  of  the  coast  and  the  direc- 
tion of  currents  and  prevailing  winds.  The  current  of  the 
Amazon  pushes' out  to  sea  and  carries  some  of  its  load  three 
hundred  miles  from  land,  as  is  indicated  by  the  muddy  color 
of  the  ocean. 


RIVERS  AND  THEIR  WORK  237 

257.  Erosion.  —  From  the  time  rain  falls  upon  the  earth 
until  it  reaches  the  sea,  the  water  is  doing  the  work  of 
erosion.  Mantle  rock  and  soft  rock  are  carried  away  grain 
by  grain,  leaving  sometimes  deep  gullies,  sometimes  pyra- 


FIG.  125.  —  THE  COLORADO  RIVER  IN  THE  GRAND  CANYON 

The  river  is  flowing  here  in  a  gorge  worn  in  granite  rock  which  is  as  old 
as  any  known.  The  highest  elevations  shown  are  not  so  high  as  the  plain 
in  which  the  work  of  erosion  began.  1.  Describe  the  rock  resting  upon  the 
granite.  2.  Give  a  reason  why  the  valley  is  wider  at  the  upper  levels. 
3.  What  may  have  become  of  the  material  removed  from  this  valley? 

mids  or  irregular  columns  of  material  slightly  harder  than 
the  rest.  Erosion  continues  to  take  place  after  the  stream 
is  formed.  The  grains  of  sand  carried  by  the  current  wear 
upon  the  bed  or  banks  of  the  river  and  scour  them,  as 
sandpaper  rubs  off  wood  or  soft  stone. 

The  Colorado  River  shows  remarkable  results  of  erosion 


238     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

in  its  hundreds  of  miles  of  water-worn  canyons,  thousands 
of  feet  deep.  Its  velocity  is  so  great  that  it  carries  coarse 
sand  and  even  large  pebbles.  The  St.  Lawrence  River  is 
in  direct  contrast  to  both  the  Mississippi  and  the  Colorado. 
It  neither  deposits  sediment  in  its  bed  nor  erodes  by  means 
of  what  it  carries.  Its  waters  have  flowed  through  lakes 
whose  quiet  depths  have  received  the  transported  material, 
leaving  clear  water  to  flow  on  to  the  sea. 


FIG.  126.  —  A  FLOOD  SCENE 

A  railroad  bridge  and  its  abutments  have  been  carried  away.  The 
position  of  the  tracks  is  evidence  of  the  force  of  the  current.  What 
shows  the  direction  of  the  current? 

258.  Deposit. —  By  depositing  the  material  that  it  car- 
ries, a  river  may  build  up  its  bed  and  its  banks;  at  the 
mouth  it  may  form  a  delta  and  sand  bars.  At  flood  times, 
when  torrential  rains  or  melting  snows  in  the  spring  have 
caused  the  river  to  overflow  its  banks,  the  receding  water 
leaves  a  thin  layer  of  mud  on  the  land.  Wherever  the 
velocity  of  the  current  is  decreased,  some  material  is  de- 
posited in  the  river  bed,  and  thus  sand  bars  are  formed. 


RIVERS  AND  THEIR  WORK 


239 


These  bars  may  become  permanently  joined  to  the  shore  or 
may  remain  as  islands. 

The  Mississippi  River,  flowing  very  slowly  in  its  lower 
course,  has  been  filling  up  its  channel.  As  the  bed  of  the 
stream  has  thus  been  raised,  the  water  would  in  many  places 
overflow  the  banks  every  year  if  artificial  banks  (called 


FIG.  127.  —  EROSION  OF  ELEVATED  SURFACES,  MONUMENT  PARK, 

COLORADO 

This  is  a  stratum  of  coarse  sandstone  which  had  a  layer  of  harder 
rock  over  it.  In  its  elevation,  vertical  cracks  were  made,  and  erosion  re- 
sulted in  the  making  of  columns.  How  was  this  assisted  by  freezing  water? 

levees)  had  not  been  built.  The  levees  must  be  high  enough 
to  restrain  the  water  at  flood  times.  The  higher  the  river, 
the  greater  pressure  there  is  against  the  side  of  the  levee. 
Constant  watch  is  maintained  when  the  river  is  full,  in  order 
to  prevent  disastrous  breaks,  and  millions  of  dollars  are  spent 
annually  to  prevent  and  repair  damage. 

The  Ohio,  the  Arkansas,  the  Amazon,  and  the  Yellow 
rivers  have  great  floods.  In  thickly  populated  China,  the 
loss  of  life  is  often  great  and  the  destruction  of  rice  fields 
results  in  famine.  On  the  other  hand,  the  flood  of  the 


240      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

Nile  in  Egypt,  which  formerly  occurred  annually,  has  been 
a  real  benefit  to  the  land.  It  has  deposited  the  fertile  soil 
upon  which  depends  the  support  of  millions  of  people.  The 
great  dam  at  Assouan  now  holds  back  the  water,  so  that 
it  may  be  distributed  by  irrigating  canals. 

259.  Changes  in  the  Continents. —  It  is  said  that  the 
sediment  deposited  in  one  year  by  the  Mississippi  would 
make  a  pyramid  half  a  mile  square  and  seven  hundred  feet 
high  —  a  small  mountain,  in  fact.     This  material  must  have 
been  removed  from  the  land  through  which  the  river  and  its 
tributaries  flowed.      What  the  Mississippi  is   doing,  other 
rivers  are  doing  to  a  lesser  degree.     That  means  that  the 
mountains  have  been  lowered  and  the  hillsides  have  lost  some 
of  the  slowly  made  soil — perhaps  only  the  fraction  of  an  inch; 
but  the  final  result  must  be  the  lowering  and  leveling  of 
the  continents.     By  the  work  of  rivers,  mountains  become 
rounded  and  low,  valleys  are  filled,  and  the  borders  of  conti- 
nents   are    extended.       (LABORATORY    MANUAL,     Exercise 
XXII.) 

260.  The  Usefulness  of  Rivers. —  Rivers  are  invaluable 
to  pioneers  in  opening  up  a  new  country.     They  furnish  an 
easy  means  of  traveling  and  of  carrying  supplies,  and  often 
penetrate  forests  otherwise  impassable.     After  settlement  is 
completed,  they  continue  to  furnish  the  cheapest  means  of 
carrying  freight. 

The  shorter,  swift-flowing  rivers,  which  are  not  navigable 
because  of  falls  and  rapids,  are  useful  for  the  power  they 
furnish  to  run  machinery.  The  great  rivers  often  have 
rapids  in  their  upper  courses,  where  they  are  known  as  young 
rivers,  because  of  their  velocity,  great  erosive  power,  and  un- 
even bed.  The  mature  streams,  characterized  by  gentle  flow, 
greater  volume,  and  absence  of  rapids,  transport  fine  rock 
waste  which  the  younger  part  of  the  stream  has  brought  in. 
They  carry  upon  their  surface  millions  of  dollars  of  freight 
from  the  interior  to  the  seaports. 


RIVERS  AND  THEIR  WORK 


241 


Knowing  the  character  of  the  towns  and  cities  upon  a 
river,  one  can  tell  which  is  the  youthful  and  which  the 
mature  part.  Manufacturing  places  on  the  borders  of  the 
young  working  river  are  followed  lower  down  by  centers  of 
commerce  and  trade  on  the  mature  navigable  stretch. 

261.  The  Absence  of  Rivers. —  A  land  without  rivers  is 
usually  a  desert.  The  principal  reason  for  the  absence  of 


FIG.  128.  —  SPRUCE  TREE  CANYON,  MESA  VERDE,  COLORADO 

1.  What  are  the  signs  of  surface  drainage  into  the  valley?  2.  How 
has  weathering  changed  the  side  of  the  valley?  3.  What  is  the  cause  of 
the  horizonal  caverns?  One  of  them  contains  ruins  of  a  village  deserted 
long  before  the  Spaniards  discovered  them  400  years  ago. 

rivers  is  that  the  winds  blowing  from  the  great  source  of 
vapor,  the  ocean,  lose  their  moisture  before  reaching  the 
interior  of  the  continent.  If  the  warm  vapor-laden  winds 
encounter  a  range  of  mountains,  the  air  cools  as  it  rises,  and 
the  vapor  condenses.  Rain  falls  on  the  slopes  of  the  moun- 
tain nearest  the  ocean.  Here  there  are  forests,  mountain 
streams,  and  peaks  whose  melting  snow  keeps  the  supply 


242      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

of  water  constant  on  that  side.  On  the  other  side  is  the 
desert. 

262.  Irrigation. —  There  are  thousands  of  square  miles  of 
land  in  the  United  States,  as  well  as  elsewhere,  which  have 
long  been  considered  worthless  and  have  been  both  impass- 
able and  uncultivated  because  of  desert  conditions.  It  has 
always  been  known  that  the  land  bordering  a  stream  is  more 
fertile  than  similar  areas  at  a  distance  from  the  stream. 
By  diverting  a  part  of  the  water  of  streams  into  a  system 
of  canals  and  ditches,  a  much  larger  area  can  be  artificially 
watered.  This  method  of  supplying  water  is  called  irriga- 
tion. By  its  practice,  in  the  last  fifty  years  much  of  the 
desert  in  this  country  has  been  reclaimed  for  cultivation. 

The  United  States  Reclamation  Service  and  some  private 
enterprises  are  conducting  extensive  systems  of  irrigation  in 
the  region  between  the  Rocky  Mountains  and  the  Sierra 
Nevadas.  They  have  secured  possession  of,  or  the  right  to 
take  water  from,  streams  whose  headwaters  are  at  a  con- 
siderable elevation  above  the  lands  to  be  irrigated.  In 
some  places  reservoirs  are  built  to  accumulate  water  during 
the  spring,  the  time  of  freshets  and  melting  snows.  The 
water  passes  by  gravity  from  the  reservoirs,  or  streams, 
through  canals  and  ditches  and  sometimes  by  tunnels 
through  mountains,  to  the  arid  region.  At  intervals,  gates 
are  provided  by  which  water  can  be  let  out  into  a  canal 
on  a  lower  level.  From  this  canal,  water  flows  through 
parallel  trenches  all  over  a  great  farm. 

Many  sections  of  eastern  Colorado,  Utah,  New  Mexico, 
Arizona,  and  southern  California  are  now  producing  mel- 
ons, peaches,  oranges,  and  lemons,  as  well  as  sugar  beets 
and  all  kinds  of  garden  produce.  A  few  years  ago  these 
regions  bore  only  sage  brush  and  cactus  and  were  the  homes 
of  the  prairie  dog,  the  scorpion,  and  the  coyote. 


RIVERS  AND  THEIR  WORK  243 


EXERCISES 

1.  How  does  the  presence  of  soil  and  mantle  rock  help  in  the 
formation  of  rivers? 

2.  (a)  What  is  the    load  of    a  river?     (6)  Where   does  it  come 
from?     (c)  What  becomes  of  it? 

3.  Make  a  comparison  between  any  two  rivers  you  know:     (a) 
in  regard  to  their  load;    (b)  in  regard  to  the  work  they  do. 

4.  If  the  sediment  at  the  bottom  of  a  slow  stream  were  consoli- 
dated, what  kind  of  rock  would  be  made? 

6.  Why  are  pebblef  in  the  bed  or  on  the  banks  of  some  streams 
rounded  and  smooth? 

6.  Why  are  there  more  pebbles  of  quartz  than  of  other  minerals? 

7.  When  a  river  meets  an  obstruction,  why  does  it  flow  around 
instead  of  over  the  obstruction? 

8.  Describe  a  method  by  which  you  could  find  out  very  nearly 
how  fast  a  stream  flowed. 

9.  Why  are  swift  streams  straighter  than  slow  ones? 


CHAPTER  XXI 
GLACIERS    AND    LAKES 

263.  The   Snow  Line. —  Whenever  the  temperature  of 
the  air  is  below  the  freezing  point,  if  much  water  vapor  is 
present,  crystals  of  ice  form  and  fall  singly  or  in  groups, 
called  snowflakes.     These  sometimes  melt  in  passing  through 
warm  air  near  the  earth  and  then  fall  as  rain,  but  in  cold 
climates  they  reach  the  earth  as  snow.     At  very  high  alti- 
tudes, even  in  the  tropics,  the  mountains  and  plateaus  may 
be  perpetually  covered  with  snow.     The  summer  limit  of  the 
snow  is  called  the  snow  line.     In  winter,  of  course,  the  snow 
line  is  lower  down  the  mountain  than  at  other  seasons.     In 
summer  numerous  waterfalls  on  the  mountains  testify  to 
the  melting  of  the  snow  back  to  a  higher  line. 

264.  The  Beginning  of  a  Glacier.  —  Above  the  summer 
snow  line,  the  snow  by  its  own  weight  becomes  more  and 
more   densely  packed.     As  the  air  between  the  flakes  is 
pressed  out,  the  snow  loses  its  white  look  and  becomes 
almost  like  ice.     Where  this  takes  place  on  a  slope,  the  ice 
begins  to  move  slowly  downward  in  a  broad  or  narrow  sheet, 
according  to  the  form  of  the  land  beneath.     Such  moving 
ice  is  a  glacier.     It  may  extend  many  miles  down  the  valley, 
as  is  the  case  with  several  glaciers  in  Alaska,  Norway,  and 
Switzerland. 

A  high  plateau  may  be  covered  with  an  ice  sheet  which 
moves  very  slowly  in  all  directions  from  its  highest  part. 
A  large  part  of  a  continent  may  be  covered  with  moving 
ice,  as  happened  in  the  northern  part  of  North  America 
many  thousand  years  ago  and  as  is  the  case  in  Greenland 
to-day. 

244 


GLACIERS  AND  LAKES 


245 


FIG.  129.  —  GLACIERS  IN  A  VALLEY  IN  SWITZERLAND 

This  is  a  summer  view  of  peaks  perpetually  covered  with  snow.  1.  A 
glacier  fills  a  steep  valley  between  the  peaks.  What  seems  to  be  its  lower 
limit  in  winter?  2.  Why  are  there  so  many  waterfalls  among  the  Alps? 

265.    The  Work  of  Moving  Ice. —  Rock  waste  beneath 
the   glacier   becomes   frozen   into   the   ice   and   is  like    a 


246     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

tool  held  in  a  firm  grasp,  scraping  and  chiseling  the  rock 
beneath.  Erosion  takes  place  in  the  bed  of  the  glacier  and 
along  the  sides  of  the  valley.  Rocks  and  earth,  brought 
by  avalanches  to  the  surface  of  the  glacier,  are  carried 
along  by  the  moving  ice.  As  the  lower  end  of  the  glacier 
is  always  melting  in  the  warm  season,  the  rubbish  lying  on 


FIG.  130.  —  SNOW  FIELD  AND  GLACIER 

This  glacier  comes  from  the  high  Alps.  The  mountains  are  so  steep 
that  snow  cannot  rest  upon  their  peaks.  1.  How  are  the  snow  fields  formed? 
2.  How  do  you  account  for  the  roughness  of  the  surface  of  the  glacier? 

the  surface  and  embedded  in  the  ice  falls  at  the  end  of  the 
glacier.  The  material  deposited  in  a  ridge  at  the  end  is 
known  as  the  terminal  moraine. 

266.  The  Retreat  of  a  Glacier.— Where  a  distinct  ridge 
of  mixed  coarse  and  fine  rock,  sand,  and  clay  is  found  across 
an  old  valley  or  stretching  over  a  continent,  it  indicates  the 


GLACIERS  AND  LAKES  247 

end  of  an  old  glacier.  The  glacier  long  ago  retreated  from 
a  former  position  and  left  moraine  material  where  the  ice  had 
been  melting.  This  does  not  mean  that  the  glacier  moved 
backward,  but  that  the  end  melted  faster  than  the  glacier 
advanced  and  thus  each  season  the  glacier  receded  farther  up 
the  valley,  nearer  its  source  than  the  last  season.  Such  will 
be  the  history  of  a  glacier  if,  because  of  change  in  climate  or 


FIG.  131.  —  GLACIATED  ROCK 

This  is  hard  trap  rock  exposed  on  the  top  of  a  hill.  1.  Two  sets  of 
lines  are  shown  on  the  rock.  Which  were  made  by  the  glacier?  How 
do  you  judge?  2.  If  the  thin  layer  of  soil  covering  parts  of  the  rock  were 
removed,  do  you  think  glacial  marks  would  be  found  upon  it?  Why? 

elevation,  there  is  a  decrease  in  the  supply  of  snow,  whose 
weight  causes  the  glacier  to  move.  Many  glaciers  in  the 
United  States  are  known  to  have  retreated  to  the  summits 
of  the  Rocky  and  Sierra  Nevada  mountains.  There,  melt- 
ing during  the  summer,  they  now  furnish  a  permanent  source 


248     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

of  water,  which  is  stored  and  used  for  city  water  supply, 
for  irrigation,  or  for  hydraulic  mining. 

267.  Drift. —  The  rock  fragments,  sand,  and  clay  which 
a  moving  ice  sheet  carries,  are  all  left  on  the  land  beneath 
when  the  ice  melts.     This  deposit  is  called  drift.     It  covers 
the  northern  United  States  as  far  west  as  the  Rocky  Moun- 
tains and  as  far  south  as  the  Ohio  and  Missouri  rivers. 
The  British  Isles,  Scandinavia,  and  parts  of  Germany  are 
covered  with  a  similar  deposit.     In  river  valleys,  the  drift 
has  been  covered  by  deposits  of  flood  material,  but  it  may 
still  be  seen  on  hillsides  and  even  on  high  ridges  where 
are  scattered  loose  stones,  more  or  less  rounded  in  shape, 
varying  in  size  from  a  pebble  to  a  small  house.     The  large 
stones  are  called'  boulders.    They  are  often  totally  unlike  any 
other   rock  within  many  miles,   but  are   similar   to  rocks 
found  farther  north.      The  location  of  such  boulders  and 
the    direction    of    scratches    upon    rocks   over    which    the 
glacier  passed,  have  helped  to  determine  the  direction  in 
which   the    ancient   North  American    ice   sheet    moved  — 
in  general,  toward  the  south. 

268.  Glacial  Lakes. —  If  you  examine  a  map  of  any  of 
the  New  England  or  other  northern  states,  you  find  many 
small  lakes  scattered  over  the  country,  while  in  the  southern 
and  middle  states  there  are  very  few.     Some  of  the  lakes 
lie  among  hills;  some  are  in  the  plains.     The  making  of 
lake  basins  is  an  important  work  of  a  glacier. 

In  its  progress,  the  ice  with  its  rock  tools  scooped  out  hollows 
in  the  softer  rocks,  and  after  the  ice  withdrew,  the  basin  was  a 
receptacle  for  water  from  the  hillsides  around.  Such  lakes 
are  found  in  the  Highlands  of  Scotland,  in  the  Swiss  and 
Italian  Alps,  in  Canada,  and  in  some  of  the  northern  states. 

The  terminal  moraine  sometimes  makes  a  dam  across  a 
valley  and  thus  forms  a  basin  to  receive  drainage.  Lakes 
made  in  this  way  are  usually  long  and  narrow.  All  of  the 
Great  Lakes,  except  Lake  Superior,  were  probably  the  re- 


GLACIERS  AND  LAKES  249 

suit  of  glacial  obstruction.  Most  of  the  lakes  in  the  north- 
ern states  result  from  irregularities  in  the  surface  of  the 
drift  deposited  by  the  ice  sheets.  Minnesota  and  Wisconsin 
are  dotted  with  lakes  of  this  type. 

There  is  still  another  kind  of  lake  which  is  glacier-formed. 
When  the  ice  of  a  glacier  is  thickly  covered  with  earth  and 
stone  —  as  are  parts  of  the  Malaspina  glacier  in  Alaska, 


FIG.  132.  —  LAKE  LOUISE,  A  GLACIAL  LAKE 

There  are  no  lakes  more  beautiful  than  glacier  lakes.  1.  Name  two 
ways  in  which  their  basins  have  been  prepared  by  glacial  action.  2.  What 
is  the  source  of  their  water?  3.  Why  is  the  water  that  enters  them  often 
muddy?  4.  Why  is  the  outflow  clear? 

upon  which  forests  are  growing, —  the  covering  prevents 
melting  in  that  portion  of  the  glacier.  During  the  melting 
of  the  rest  of  the  glacier,  deposits  are  made  around  the 
unmelted  area.  After  a  long  time,  it  too  is  melted  and 


250     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

the  water  sinks  into  the  ground,  leaving  a  hollow  where 
the  ice  was.  This  may  fill  and  form  a  pond  or  small  lake. 
Such  hollows,  if  they  are  not  filled  with  water,  are  known 
as  "  kettle  holes,"  because  of  their  rounded  form., 

269.  Other  Causes  of  Lakes. —  Some  lakes  —  like  Lake 
Superior,  lakes  in  Central  Asia,  and  lakes  in  Africa  —  were 
formed  in  basins  left  when  elevations  were  made  in  the 
earth's   crust.     Others,    like    Crater   Lake   in   Oregon,    fill 
the  craters  of  extinct  volcanoes.     Still  others  were  formed 
by   the   damming    of    a   river    by  a   landslide   or   a   lava 
flow. 

270.  Lakes  as  Sources  of  Rivers.  —  When  the  basins, 
formed  as  described,  have  filled  with  water  up  to  the  lowest 
part  of  their  walls,  the  water  of  course  flows  out  at  that  point 
and  the  lake  then  becomes  the  source  of  a  stream.    If  a  lake 
"  has  no  outlet/'  as  is  sometimes  said,  the  water  will  eventu- 
ally become  salt.     Many  lakes  which  apparently  have  no 
outlet,   discharge  their  water  through  passages  from  the 
bottom  or  sides  of  the  lake  into  underground  streams,  and 
thus  remain  fresh  water  lakes. 

271.  Uses  of  Lakes.  —  Many  lakes  furnish  abundant  sup- 
plies of  fish  for  food.     They  also  add  greatly  to  man's 
pleasure  by  their  beauty  and  by  their  facilities  for  boating 
and  bathing.     The  large  lakes  modify  the  extremes  of  heat 
and  cold  in  surrounding  land,  as  do  the  oceans.     If  a  lake 
is  situated  in  an  elevated  region,  its  water  may  be  carried 
long  distances  in  pipes,  to  be  used  for  power  or  for  supply- 
ing domestic  needs  in  cities. 

272.  Reservoirs.  —  The  commercial  use  of  lakes  has  led 
to  the  making  of  artificial  lakes  or  reservoirs  by  building 
dams  across  the  outlets  of  a  basin  and  thus  holding  back 
the  water  that  enters  it.     There  may  be  many  millions  of 
gallons  of  water  flowing  daily  into  the  reservoir  from  con- 
stant springs  and  streams  draining  many  square  miles  of 
territory. 


GLACIERS  AND  LAKES  251 

Reservoirs  may  be  constructed  many  miles  away  from  the 
city,  and  the  water  may  be  carried  in  open  canals  or  in 
closed  pipes.  The  pipes  may  pass  through  a  mountain  or 


FIG.  133.  —  SUPPLYING  A  CITY  WITH  WATER 

The  dotted  line  is  part  of  the  boundary  of  the  region  which  supplies 
most  of  the  water  to  the  two  streams  flowing  east.  The  shaded  portion  is 
the  area  of  a  possible  reservoir  having  natural  hillside  boundaries.  If  dams 
or  embankments  are  built  at  three  places,  d,  the  waters  of  the  two  streams 
will  be  held  back.  1.  What  is  the  elevation  of  the  contour  line  bounding 
the  reservoir?  2.  What  must  be  the  level  of  the  top  of  the  dams?  3. 
The  southern  stream  flows  now  at  d,  at  an  elevation  of  about  400  ft.  If  a 
dam  is  built  there,  how  high  must  it  be? 

under  a  river,  even  up  and  down  hill,  always  provided  that 
no  part  of  the  pipe  is  as  high  as  the  source  of  the  water  it 


252      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

carries.  In  1873  the  city  of  Vienna  was  supplied  with 
water  from  the  Alps,  seventy  miles  away.  That  was  one  of 
the  first  enterprises  of  the  kind.  Water  is  now  carried  a 
much  greater  distance  from  the  mountains  to  Los  Angeles, 
San  Francisco,  and  other  cities. 

Natural  water  is  not  chemically  pure,  but  for  domestic 
uses  it  should  be  clean.  It  is  made  clean  by  filtering  it 
through  beds  of  sand  and  gravel  constructed  between  the 
receiving  or  storage  reservoir  and  the  distributing  reservoir. 
The  filtering  removes  some  minute  organisms  and  sedi- 
ment. As  disease  germs  are  too  small  to  be  removed  by 
filtering,  they  must  be  prevented  from  entering  the 
reservoir  by  keeping  the  drainage  basin  clear  of  all 
dwellings,  camps,  and  cattle.  State  laws  give  to  cities 
and  towns  the  right  to  remove  all  buildings  from  land  which 
has  been  selected  for  a  basin  to  furnish  a  water  supply. 
Suitable  compensation,  of  course,  is  made  to  the  owners. 

In  the  region  of  the  great  central  plain,  where  in  many 
towns  the  people  depend  on  wells  for  water  supply,  the 
same  care  should  be  taken  to  prevent  pollution  of  the 
water.  Many  large  cities  use  river  or  lake  water  which 
has  been  exposed  to  contamination.  In  such  cases,  chemi- 
cal means  are  sometimes  used  to  destroy  germs  and  purify 
the  water.  (LABORATORY  MANUAL,  Exercise  XXIII.) 

EXERCISES 

1.  Describe  the  beginning  of  a  glacier. 

2.  Where  is  the  glacier  that  is  nearest  to  your  home? 

3.  Are  there  glaciers  on  mountains  in  your  state?     Why? 

4.  What   change  of   conditions  of  the  earth's  surface  or  of  the 
atmosphere  might  cause  a  glacier  to  form  in  the  Allegheny  Mountains? 

6.  How  do  people  know  that  a  glacier  once  covered  North  America 
as  far  south  as  the  Ohio  River? 

6.  Where  are  there  now  great  glaciers  in  North  America? 

7.  Moving  at  an  average  rate  of  20  in.  a  day  and  melting  22  in., 
how  would  the  end  of  a  glacier  change  position   from  April   1   to 
October  1?  '*• 


GLACIERS  AND  LAKES  253 

8.  What  is  such  a  change  of  position  (described  in  Ex.  7)  called? 

9.  What  rate  of  motion,  allowing  for  no   melting,  would   bring 
the  glacier  of  Ex.  7  back  in  6  months  to  the  position  of  April  1? 

10.  How  are  long  narrow  lakes  sometimes  formed? 

11.  Name  two  other  ways  in  which  lakes  are  made. 

12.  How  must  a  lake  be  situated  to  furnish,  by  gravity,  a  water 
supply  for  a  city? 

13.  Why  is  the  water  salt  in  lakes  having  no  outlet? 


CHAPTER  XXII 
LIVING  MATTER 

273.  Physiological   Properties.  —  Plants  and  animals  are 
made  up  of  matter,  and  have  certain  physical  properties, 
such  as  weight  and  extension,  which  are  possessed  by  all 
matter.     In  addition  to  physical  properties,  both  plants  and 
animals  possess  certain  properties  which  never  belong  to 
non-living  matter.     These  are  called  physiological  properties; 
they  are  irritability,  spontaneous  motion,  reproduction,  and 
nutrition.     Any  body  possessing  these  properties  is  called  an 
organism,  and  much  of  the  material  of  which  it  is  composed 
is  called  organic  material. 

274.  Irritability.  —  Both  plants  and  animals  respond  to 
influences  from  without.     For  example,  leaves  turn  toward 
the  source  of  light,  and  the  odor  of  food  will  make  a  dog's 
mouth   water.     This   property   of   responding   to    external 
conditions  is  called  irritability. 

275.  Spontaneous  Motion.  —  Both   plants   and   animals 
have  the  power  to  change  the  position  of  parts  of  the  body 
or  the  whole  body.     This  is  the  property  of  spontaneous 
motion.     A  fish  darts  rapidly  or  moves  slowly  through  the 
water  at  will.     Plants  move  their  leaves,  stems,  flowers,  or 
other  parts,  but  generally  so  slowly  as  to  be  unnoticed  in 
brief  observation. 

276.  Reproduction.  —  Both  plants  and  animals  possess  the 
property  of  reproduction;  that  is,  they  can  form  other  bodies 
like  themselves.     For  example,  the  bean  plant  reproduces  by 
means  of  seeds,  and  the  fish  by  means  of  eggs. 

277.  The   Need   of   Energy.  —  These  three  properties  — 
irritability,  spontaneous  motion,   and  reproduction  —  con- 

254 


LIVING    MATTER 


255 


stitute  the  functions  or  work  done  by  the  animal  or  plant. 
Work,  whether  it  is  done  by  a  machine  or  a  living  thing,  re- 
quires energy  or  work-power  for  its  performance.  A  ma- 
chine may  obtain  energy  for  working  from  electricity,  or 
from  falling  water,  or  from  the  oxidation  of  fuel.  The  oxida- 
tion in  the  body  of  a 
plant  or  animal  may  be 
compared  with  the  proc- 
ess which  goes  on  in  the 
firebox  of  a  steam  en- 
gine. The  burning  of 
fuel  causes  heat,  which 
makes  steam .  Steam 
has  energy;  that  is,  it 
can  do  work  when  prop- 
erly employed  in  a  ma- 
chine. The  energy  by 
means  of  which  plants 
and  animals  perform 
their  physiological  func- 
tions is  always  derived 

c  '**  a 

134.  —  THE  VENUS  FLY  TRAP 


from  the  oxidation  of 
some  of  the  material 
found  in  the  working 
part.  If  oxidation 
ceases,  there  can  be  no 
energy  and  life  is  at  an 
end. 

278.  Nutrition. — Food 
is  the  name  given  to  sub- 
stances that  furnish  ma- 
terials  by  which  an 


a 


FIG. 


Under  ordinary  conditions,  the  end  of 
the  leaf  is  spread  out  flat  as  in  position  a. 
The  edges  of  Ihe  leaf  are  toothed;  the 
inside  is  covered  with  hair-like  projections. 
If  these  projections  are  touched  lightly, 
as  with  a  straw,  the  leaf  slowly  folds 
together  as  in  b,  and  finally  as  in  c.  If  a 
small  insect  crawls  on  the  leaf,  he  is  shut 
within.  The  plant  absorbs  food  from  his 
decaying  body;  after  some  days  the  leaf 
opens  again  and  the  thin  shell  of  his  body 
is  all  that  remains.  What  properties  of 
living  matter  are  thus  illustrated? 


organism   makes   new 

structures  or  repairs  old  ones  in  its  body,  and  to  substances 

that  can  be  oxidized  to  give  energy  to  the  organism.     Ani- 


256      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


mals  and  plants  possess  the  property  of  taking  up  such  sub- 
stances.    This  property  of  taking  food  and  converting  it  into 

energy  or  the  material  of  the 
body  is  nutrition. 

The  food  of  the  young 
plant  is  mainly  starch,  a 
compound  of  carbon, 
hydrogen,  and  oxygen;  and 
proteid,  which  is  a  compound 
of  these  elements  with 
nitrogen  and  traces  of  others. 
This  food  material  is  stored 
in  the  seed  and  from  it,  to- 
gether with  water  absorbed 
from  the  ground,  is  formed 
the  material  of  the  first  root, 
stem,  and  leaves  of  the  plant. 
Some  plants  grow  many  inches 
in  height  with  no  food  but 
that  in  the  seed.  The  newly 
hatched  fish  or  chicken,  turtle 
or  bird,  has  grown  to  a  con- 
siderable size  from  the  ma- 
terial stored  within  the 


FIG.  135.  —  GROWTH  FROM  FOOD 
STORED  IN  THE  SEED 

A  garden  pea  was  sprouted  in 
a  damp  place.  It  was  then  placed 
so  that  the  sprout  passed  through 


egg- 
But  the  life  processes  can- 


hole   in   a   piece   of    cheese-cloth     not  Continue  Without  energy, 


stretched  over  a  tumbler  of   water.     &       more  than  a  machine  can 

Fig.     135    represents    a    growth    of 

several  days.    The  roots,  stem,  and     run    Without    power. 

leaves  have  developed. 

they  been  made  from? 


As  we 
what  have    jiaye  geen?  energy  is  derived 

from  oxidation.  The  food 
provides  the  material  to  be  oxidized,  but  oxygen  also  is 
necessary.  The  power  to  take  oxygen,  or  respiration,  is  a 
part  of  the  property  of  nutrition.  Respiration  is  much 
more  noticeable  in  animals  than  in  plants,  * 


LIVING    MATTER  257 

279.  The    Need    of    Food.  —  Response  to  outside  influ- 
ences, motion  of  a  part  of  the  body  or  the  whole  body,  diges- 
tion of  food,  and  formation  of  other  bodies  like  themselves, 
are  the  physiological  properties  of  plants  and  animals.     Each 
of  these  processes  is  work,  and  requires  energy.     Energy  can 
be  obtained  by  living  things  only  from  oxidation;  oxidizable 
material  (which  is  provided  by  food)  and  oxygen  are  neces- 
sary for  oxidation.     Therefore  all  living  things  require  food 
and  oxygen.     (LABORATORY  MANUAL,  Exercise  XXIV). 

280.  Amounts    of   Food   Required.  —  Plants  require  less 
food  than  animals  because  they  do  less  work  in  performing 
their  functions  than  animals   do.     The  temperature  of  a 
growing  plant  is  slightly,  if  at  all,  higher  than  that  of  the 
surrounding  air.     Its  temperature  averages  much  lower  than 
that  of  many  animals  living  under  the  same  conditions. 
Hence  less  oxygen  is  needed  by  plants  in  respiration  and  less 
food  material  is  needed  as  fuel. 

All  animals  do  not  require  the  same  amount  of  food.  The 
robin  is  an  active,  rapidly  moving  organism;  a  toad  is  inac- 
tive much  of  the  time.  Therefore  a  robin  needs  more  energy 
than  a  toad  and,  consequently,  more  food. 

281.  Waste  Products  from  Oxidation.  —  When  the  coal 
in  a  furnace  is  brought  to  the  kindling  temperature,  its  prin- 
cipal constituent,  carbon,  unites  with  oxygen,  and  heat  energy 
is  released.     The  gas,  carbon  dioxide,  which  is  not  only  of 
no  assistance  to   combustion,  but  is  *a  positive  hindrance, 
passes  off.     It  is  called  a  waste  product. 

A  similar  process  takes  place  in  the  body  of  a  plant  or  ani- 
mal. Carbon  is  an  element  in  many  kinds  of  food  and  be- 
comes a  part  of  the  body  itself.  This  body  material  unites 
with  the  oxygen  taken  in  by  the  plant  or  animal  to  produce 
energy  and,  just  as  in  the  furnace,  carbon  dioxide  is  formed. 
As  this  gas  cannot  be  used  and  is  injurious  when  retained  in 
the  body  of  the  plant  or  animal,  it  is  a  waste  product  and  is 
given  off  from  the  breathing  organs  of  animals  and  from  the 


258      FIRST  YEAR   COURSE   IN   GENERAL  SCIENCE 

leaves  of  plants.  There  are  other  waste  products  which  are 
disposed  of  in  different  ways.  The  removal  of  waste  pro- 
ducts which  would  hinder  oxidation  is  a  part  of  nutrition;  the 
process  is  called  excretion. 

282.  Residue   Left   from   Food.  —  When  coal  is  the  fuel 
used  in  a  furnace,  besides  the  waste  product  in  the  form  of 
gas,  there  is  a  residue  which   can  not   be  oxidized  to  give 
heat.     This  residue  of  clinkers,  stones,  and  ashes  cannot  be 
burned,  and  is  of  no  use  as  fuel.     The  bodies  of  living  things 
take  in,  with  their  food,  substances  which  never  become  a  part 
of  the  body  and  are  never  oxidized.     This  residue  is  expelled 
from  animal  bodies  from  the  lower  end  of  the  intestine; 
in  plants  it  collects  in  the  leaves  and  is  removed  when  the 
leaves  fall. 

283.  Protoplasm. — No  matter  how  different  from  one  an- 
other the  many  forms  of  plant  and  animal  life  may  be,  they 
are  all  alike  in  one  particular:  they  are  largely  composed  of 
a  kind  of  matter  called  protoplasm.     Protoplasm  is  not  life 
itself,  but  it  is  the  only  material  in  which  life  is  known  to 
occur.     Protoplasm  is  a  colorless  liquid,  nearly  transparent, 
about  as  thick  as  the  white  of  a  raw  egg.     There  are  minute 
living  bodies  which  consist  of  nothing  but  protoplasm.     Most 
living  things,  however,  consist  of  protoplasm  and  certain 
other  substances  made  by  it,  such  as  sugar,  fat,  the  wood  of 
a  plant,  or  the  shell  of  an  oyster. 

284.  The  Composition  and  Behavior  of  Protoplasm.  — 
Chemists  have  studied  the  composition  of  protoplasm  and 
have  found  it  to  be  very  complex.     It  is  made  up  of  a  num- 
ber of  compounds,  which  contain  some  of  the  commonest 
elements  occurring  in  the  air,  in  water,  and  in  the  earth's 
crust.     These  are  carbon,  hydrogen,  oxygen,  nitrogen,  sul- 
phur, and  phosphorus. 

All  protoplasm,  whether  in  plants  or  animals,  has  the  same 
appearance,  the  same  chemical  composition,  and  the  same 
physiological  properties.  But  there  must  also  be  certain 


LIVING    MATTER  259 

differences,  not  yet  understood,  for  protoplasm  does  not 
always  and  everywhere  behave  in  the  same  way,  or  perform 
the  same  kind  of  work. 

The  protoplasm  in  the  tip  of  the  stem  of  a  plant  causes 
growth  toward  the  light;  that  in  the  root  causes  growth 
away  from  the  light.  The  protoplasm  in  a  sweat  gland 
under  the  skin  makes  perspiration,  while  that  on  the 
outside  of  a  clam  or  an  oyster  makes  shell.  The  great 
number  of  variations  of  life  found  among  plants  and 
animals  —  all  of  them  composed  of  the  same  living  sub- 
stance, protoplasm,  —  must  be  due  to  differences  in  the  way 
in  which  protoplasm  does  its  work  and  not  to  differences  in 
the  protoplasm  itself. 

285.  The    Necessity   for    Water.  —  Protoplasm  contains 
a  considerable  amount  of  water.     For  this  reason  all  living 
things  require  water.     The  water  lily  and  the  cactus  show, 
however,  that  there  is  a  difference  in  the  quantity  of  water 
required  by  different  plants.     Water  is  also  used  by  some 
plants  and  animals  as  a  means  of  transferring  dissolved  sub- 
stances from  one  place  in  the  body  to  another.     Sap  is  such 
a  liquid  in  plants;  blood,  in  animals. 

286.  The    Necessity   for   Food.  —  We    have    seen    that 
plants  and  animals  alike  require  food  to  furnish  materials 
from  which  new  structures  may  be  made  or  old  ones  repaired. 
Animals  must  have,  for  food,  organic  matter  already  formed; 
plants  make  their  own  food.     This  difference  distinguishes 
animals  from  plants. 

Some  plants  are  green  because  in  the  protoplasm  of  the 
leaf -cells  there  are  green  chlorophyll  bodies.  Green  plants 
take  water  from  the  soil  through  their  roots,  and  it  rises  to 
the  extremity  of  the  highest  leaf.  They  take  in  carbon  di- 
oxide through  pores  in  their  leaves.  This  is  not  breathing; 
it  is  more  like  collecting  material  to  make  food.  The  ele- 
ments contained  in  water  and  carbon  dioxide  —  namely, 
carbon,  hydrogen,  and  oxygen  —  are  made  into  food  for  the 


260      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


•proteids 


plant  by  the  action  of  the  chlorophyll  bodies,  aided  by  the 
energy  of  the  sun's  light. 

With  the  water  from  the  ground,  green  plants  take  mineral 
matter  which  has  been  dissolved  in  the  water.  Nitrates 
and  phosphates  are  mineral  matter  that  is  present  in  most 
fertile  soils.  Certain  elements  of  these  substances,  such  as 
nitrogen  and  phosphorus,  are  combined  with  the  elements 
of  sugar  and  starch,  in  green,  plants,  to  make  proteid, 

another  food.    Protoplasm 
is  made  of  proteid. 

287.  The  Relation  of 
Plants  to  Animals. — Earth, 
air,  and  water  contain  all 
the  elements  necessary  to 
the  growth  of  plants  and 
animals,  but  no  animal  can 
use  these  in  preparation  of 
food.  The  protoplasm  of 
green  plants,  with  the 
energy  of  sunlight,  makes 
food  which  is  used  by 
animals  as  well  as  by 
plants.  Animals  feed  upon 
plants  in  which  food  has 
been  made,  or  upon  other 
animals  which  have  fed 
upon  plants.  Animals  cannot  exist  without  green  plants. 
On  the  other  hand,  the  waste  product  of  animals,  carbon 
dioxide,  is  absolutely  necessary  to  plants  for  food  manufac- 
ture. 

Animals  that  eat  plants  only  are  herbivorous ;  those  that 
live  upon  other  animals  only  are  carnivorous;  while  those 
that  eat  both  plant  and  animal  food  are  omnivorous.  The 
food  of  a  sheep  and  of  a  lion  can  be  traced  to  the  same  source. 
The  food  of  a  sheep  is  proteid  matter  and  starch  found  in 


FIG.  136.  —  RELATION  BETWEEN 
PLANTS  AND  ANIMALS 

1.  Which  of  the  six  substances 
named  on  the  circle  can  be  obtained 
from  earth  and  air?  2.  How  are  the 
others  provided?  3.  Read  this  diagram 
so  as  to  express  the  dependence  of  one 
kind  of  organism  upon  the  other. 


LIVING    MATTER  261 

leaves,  stems,  and  seeds  of  plants.  This  is  made  over  into 
muscle,  fat,  and  other  tissues  which  a  lion  or  other  carnivo- 
rous animal  eats.  The  part  which  nourishes  the  lion  is  the 
proteid  and  fat  that  were  made  from  leaves  and  stems  of 
plants,  but  the  leaves  and  stems  themselves  would  not  have 
nourished  the  lion. 

288.  Permanence  of  Material  in  Organisms.  —  An 
adult  animal  in  normal  health  has  about  the  same  average 
weight  from  day  to  day.  His  weight  is  increased  by  food, 
but  this  increase  is  offset  by  the  decrease  resulting  from  the 
oxidation  of  food.  If  he  is  inactive,  his  weight  decreases 
slowly.  When  body  or  mind  is  actively  at  work,  oxidation 


FIG.  137.  —  PERMANENCE  OF  MATERIAL  IN  A  LIVING  BODY 

1.  The  dotted  line  represents  the  average  weight  of  an  organism  for 
24  hours.  2.  What  is  the  significance  of  the  rising  line  ab?  3.  What 
points  on  the  line  represent  a  condition  of  rest  after  taking  food?  Why? 
4.  What  points  represent  the  effects  of  severe  muscular  work? 

is  more  rapid  than  when  they  are  at  rest.  If  a  line  were 
used  to  show  the  weight  of  an  animal  for  twenty-four  hours, 
it  would  be  a  line  of  curves  rather  than  a  horizontal  line, 
though  its  ends  might  be  connected  by  a  horizontal  line. 

Not  only  does  the  weight  of  an  animal  vary  but  the  actual 
material  making  up  the  body  changes.  .  Parts  of  the  body  are 
removed  as  waste  products;  and  new  matter  is  taken  into 
the  body  to  replace  the  old  and  to  make  new  cells.  The 
source  of  this  new  matter  may,  for  instance,  be  a  mineral.  A 
molecule  of  limestone  may  by  several  steps  become  a  part  of 
the  body  of  a  horse.  Limestone,  when  heated  to  make  lime, 
gives  off  carbon  dioxide  into  the  air.  The  carbon  dioxide  is 
used  by  plants  in  making  starch,  which  is  found  in  seeds. 
The  seeds  which  contain  carbon  (oats  and  corn,  for  example) 
may  be  the  food  of  a  horse,  and  thus  the  carbon  once  con- 
tained in  the  limestone  becomes  part  of  a  muscle. 


262      FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 


289.  The  Cell.  —  After  the  invention  of  the  microscope 
about  the  year  1600,  people  began  to  make  use  of  its  magni- 
fying power  to  examine  all  kinds  of  plant  and  animal  sub- 
stances. It  was  not  until  1838,  however,  that  the  fact  was 
established  that  all  organisms  are  made  up  of  definitely 
formed  parts  or  units,  somewhat  in  the  manner  in  which  the 
walls  of  brick  buildings  are  made  up  of  separate  bricks. 

These  small  units  had  been  seen  two  hundred  years  earlier, 
and  at  that  time  were  called  cells,  because  it  was  thought  that 
they  were  practically  empty  spaces.  In  1838  it  was  demon- 
strated that  the  cells 
were  in  reality  separate 
masses  of  protoplasm, 
generally  surrounded  by 
an  envelope  which  is 
called  the  cell  wall.  The 
size  of  cells  varies  from 

Ts^oiy    °f    an    mch    m 
diameter  to  two  inches, 


FIG.  138.  —  Two  KINDS  OF  CELLS. 
(magnified  about  100  times) 


Figure  A  represents  two  animal  cells, 
many  of  which  make  what  we  call  a  muscle. 
Figure  B  represents  several  cells  from  the 
thin  covering  on  the  surface  of  the  body. 
There  is  one  point  of  resemblance  between 
these  two  kinds  of  cells.  What  is  it? 


the  average  diameter 
being  about  -jniW  °f  an 
inch.  The  shape  of 
cells  also  varies  greatly; 

some  are  globular,  some  flattened,  some  thread-like,  some  like 

a  pillar. 

290.  Tissues.  —  Cells  more  or  less  alike  are  often  grouped 
in  a  plant  or  animal.     Such  a  collection  of  like  cells  is  called 
a  tissue.     Examples  of  tissues  are  the  cells  of  the  skin  covering 
the  human  body,  wood  cells,  pith  cells,  and  muscle  cells. 

291.  Organs.  —  Different  kinds  of  tissue  are  often  com- 
bined to  form  a  definite  part  of  an  organism,  called  an  organ, 
such  as  a  leaf,  a  hand,  an  eye,  or  a  root.     A  leaf  consists  of  a 
thin  covering,  green  pulp,  and  veins.     There  are  more  than 
three  kinds  of  tissue  in  the  hand.     An  organ  is  a  part  of  an 
organism  which  has  a  special  kind  of  work  to  do. 


LIVING    MATTER  263 

292.  The  Importance  of  the  Cell.  —  From  what  has  been 
said  of  cells,  it  will  be  understood  that  the  work  of  an  organ  is 
really  the  result  of  the  combined  work  of  all  the  cells  which 
make  up  its  tissue.     The  contraction  of  a  muscle  is  in  reality 
due  to  the  contraction  of  every  cell  of  which  the  muscle  is 
composed.     The  cell  may  therefore  be  regarded  as  the  work- 
ing unit,  as  well  as  the  unit  of  structure. 

293.  Division    of    Labor.  —  Some  very  tiny  plants  and 
animals  have  bodies  consisting  of  but  one  cell.     Since  this 
cell  must  perform  all  the  physiological  functions  essential  to 
life,  each  function  must  be  performed  in  a  very  simple  manner. 
But  the  bodies  of  all  the  larger  organisms  consist  of  many 
cells,  among  which  the  work  of  living  is  divided.     Certain 
cells  are  concerned  with  irritability  alone,  certain  others  with 
the  taking  of  food  alone,  and  each  has  a  shape  fitted  for  the 
work  it  has  to  perform  in  order  to  support  life. 

The  single-celled  animal  or  plant  may  be  compared  to  a 
hermit,  who  must  provide  with  his  own  hands  his  shelter, 
food,  and  clothing.  A  man  living  in  a  large  city,  on  the  other 
hand,  may  purchase  all  these  necessities  from  different  people, 
each  of  whom  has  done  one  kind  of  work.  Meanwhile  the 
city  dweller  has  perhaps  been  making  tools,  or  designing  im- 
proved machinery  for  the  other  workers.  The  assignment  of 
the  necessary  work  of  life  among  different  individuals,  whether 
cells  or  complete  organisms,  is  called  division  of  labor 

294.  Division   of   Cells.  —  Most  cells  contain  a  structure 
of  denser  protoplasm,  known  as  the  nucleus.     A  cell  never 
grows  beyond  a  certain  maximum  size.     When  this  is  reached, 
the  cell  may  divide  into  two  new  cells  through  an  equal  divi- 
sion of  the  nucleus  and  the  rest  of  the  protoplasm.     Then 
each  resulting  cell  may  grow  to  the  maximum  size  of  its  kind, 
when  division  may  take  place  again.     Thus,  from  one  cell 
many  cells  may  result  by  repeated  cell  division.     This  process 
is  the  usual  method  of  growth  observed  in  the  tissues  of  plants 
and  animals. 


264     FIRST  YEAR  COURSE  IN   GENERAL  SCIENCE 


IV  V 

FIG.  139.  —  DIVISION  OF  CELLS 

1.  Cell  I  has  attained  its  greatest  possible  size.  What  change  has 
begun  in  II?  2.  How  does  the  size  of  each  cell  in  V  compare  with  the  size 
of  I?  3.  What  does  this  show  about  the  method  of  growth  of  an  organism? 

When  a  new  cell,  instead  of  helping  to  make  new  plant  or 
animal  tissue,  separates  from  the  plant  or  animal  and  develops 
into  a  new  organism,  reproduction  has  taken  place.  The 
new  cell  that  left  the  tissue  of  which  it  formed  a  part  is  called 
an  egg  cell  or  a  sperm  cell. 

EXERCISES 

1.  (a)  What  are  the  physical  properties  possessed  by  all  bodies? 
(6)  What  other  properties  are  possessed  by  organisms  only? 

2.  Why  is  food  a  universal  necessity  for  all  living  things? 

3.  What  are  the  symptoms  of  starvation  in  an  animal?   In  a  plant? 

4.  Why  can  animals  live  longer  without  food  than  without  oxygen? 
6.  (a)  Why  is  breathing  necessary?      (6)  When  is  breathing  the 

slowest?     Why? 

6.  What  property  makes  possible  the  closing  of  a  flower  at  night? 

7.  Why  does  a  humming  bird  need  more  food  than  a  snail? 

8.  Give  an  illustration,  drawn  from  this  chapter,  of  the  Law  of 
Conservation  of  Matter. 

9.  Why  cannot  the  leaves  of  most  plants  live  separated  from  the 
plant? 

10.  How  could  cells  have  been  mistaken,  in  early  microscopic  study, 
for  empty  spaces? 

11.  What  is  the  object  of  reproduction? 

12.  What  makes  division  of  labor  possible  in  higher  forms  of  life? 


CHAPTER  XXIII 
THE  LIFE   OF  A  PLANT 

295.  Study    of    a   Plant.  —  We  have  learned  that  plants 
and  animals  alike  are  characterized  by  certain  life  activities 
or  functions;    namely,  nutrition,  reproduction,  irritability, 
and   spontaneous  motion.     A  common  plant  that  can  be 
grown  readily  in  a  schoolroom  will  help  us  to  understand  how 
plants  are  able  to  carry  on  these  life  activities.    A  bean  plant 
will  illustrate  the  structure  and  the  work  of  all  green  plants. 

If  we  examine  a  mature  plant,  we  notice  first  that  it  has 
several  parts  or  organs.  These  are  roots,  stems,  leaves,  and 
sometimes  flowers. 

296.  Roots.  —  If  we  dig  up  a  bean  plant,  we  note  how 
firmly  the  roots  anchor  it  to  the  ground  and  how  the  particles 
of  soil  cling  to  the  young  rootlets.     The  central  root,  which 
seems  to  be  the  downward  continuation  of  the  stem,  is  called 
the  primary  root,  and  its  branches  are  called  secondary  roots. 

297.  Extent  of  Roots.  —  The  total  length  of  the  roots  of 
an  ordinary  plant  is  much  greater  than  is  commonly  sup- 
posed, for  when  a  plant  is  pulled  up,  a  large  part  of  the  whole 
mass  of  roots  is  usually  broken  off  in  the  ground.     The  roots 
of  winter  wheat  extend  downward  seven  feet,  and  the  roots 
of  certain  trees  in  arid  countries  have  been  known  to  reach  a 
depth  of  sixty  feet.     All  the  roots  of  a  full-grown  corn  plant, 
if  cut  off  and  pieced  end  to  end,  would  reach  over  one  thou- 
sand feet,  and  a  large  squash  vine  has  several  miles  of  roots. 

298.  Functions  of  Roots.  —  Near  the  ends  of  the  roots 
are  delicate  root  hairs,  which  are  really  cells  with  very  thin 
walls.     They  look  like  a  fine  fuzz  and  are  estimated  to  be 
about  3--J-0-  of  an  inch  in  diameter.     Small  as  they  are,  the 

265 


266      FIRST  YEAR  COURSE  IN   GENERAL   SCIENCE 

plant  needs  them.  It  is  their  function  to  take  water  from 
the  ground  into  the  roots  for  the  plant's  work  of  food  making. 
If  the  roots  are  allowed  to  become  dry,  the  root  hairs,  being 
small,  are  soon  rendered  unfit  to  take  water  from  the  soil, 
and  the  plant  droops  and  usually  dies. 

Most  shade  trees  have  a  long  primary  root.     This  helps  to 
hold  the  tree  in  an  upright  position,  even  if  strong  winds  push 


FIG.  140.  —  PRIMARY  AND  SECONDARY  ROOTS 

The  figure  at  the  left  is  a  seedling  morning-glory;  at  the  right,  a  seed- 
ling oak.  1.  Compare  the  roots  in  the  two  seedlings  as  to  kind  and  number. 
2.  Which  of  these  plants  lives  more  than  one  year?  3.  What  relation  is 
there  between  the  answers  to  1  and  2? 

against  its  spreading  crown.  The  elm  tree  is  an  exception  in 
this  respect,  and  as  a  result,  it  is  much  oftener  overthrown  in 
a  gale  than  is  the  maple,  the  oak,  or  the  chestnut. 

Roots  serve  a  useful  purpose  in  holding  particles  of  soil 
together.  The  cutting  of  a  forest  from  a  hillside  is  likely 
to  result  in  the  rapid  washing  away  of  the  soil  and  in  floods. 
Large  tracts  of  valuable  land  have  been  ruined  in  this  way, 


THE    LIFE    OF    A    PLANT 


267 


by  the  removal  of  fertile  soil  and  the  formation  of  deep  gullies. 
(LABORATORY  MANUAL,  Exercise  XXV.) 

299.  Stems  and  their  Functions.  —  Stems  bear  the  leaves 
and  hold  them  out  in  the  most  advantageous  positions  for 
receiving  light  and  air.  They  also  serve  as  pathways  for 


FIG.  141.  —  SIMPLE  AND  .COMPOUND  LEAVES 

1.  Which  compound  leaf  does  A  resemble?  2.  What  would  make  the 
resemblance  closer?  3.  Compare  another  compound  leaf  with  one  of 
the  simple  ones.  4.  State  some  resemblances  in  veining  between  one  of 
the  simple  leaves  and  a  compound  leaf. 

transmitting  liquids  between  the  roots  and  the  leaves.  In 
a  very  young  plant,  the  stem  depends  largely  upon  water  in  its 
cells  to  keep  it  stiff.  In  order  that  stems  may  be  able  to  stand 
upright  and  bear  the  weight  of  branches  and  leaves,  they 
are  strengthened,  as  they  grow,  by  many  tough  fibers.  We 
are  all  familiar  with  such  fibers  in  the  ''strings"  of  celery. 


268      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


FIG.  142.  —  CELLS  FROM 
THE  SURFACE  OF  A  LEAF. 
(magnified  about  250 
times) 


300.  Leaves  and  their  Functions.  —  The  examination  of 
a  bean  plant  will  show  that  what  we  might  at  first  take  to  be 
separate  leaves  of  the  plant  are  joined  in  groups  of  three. 
These  leaflets, .as  they  are  called,  are 
really  parts  or  divisions  of  one  leaf. 
Such  a  leaf  is  called  a  compound 
leaf.  The  clover,  the  rose,  and  the 
locust  have  compound  leaves.  Most 
of  our  commonest  plants  bear  simple 
leaves.  The  elm,  the  geranium,  and 
the  lettuce  have  simple  leaves. 

The  leaves  of  a  plant  are  so  placed 
as  to  shade  one  another  as  little  as 
possible.  The  leaves  at  the  lower 
end  of  the  twig  may  have  longer 
stems  than  those  above.  In  some 
plants  leaves  grow  in  pairs  on  oppo- 
site sides  of  the  stem,  the  second 
pore  or  pair  at  right  angles  to  the  first.  If 
a  leaf  is  held  up  to  the  light,  many 
fine  branching  veins  can  be  seen. 
The  veins  of  a  leaf  are  not  like  veins 
in  an  animal — tubes  solely  for  carry- 
ing a  liquid.  They  furnish  a  frame- 
work for  the  softer  parts  of  the  leaf. 
(LABORATORY  MANUAL,  Exercise 
XXVI.) 

work  of  the  leaf.  i.  Why  Microscopic  examination  of  a  leaf 
would  the  pores  be  smaller  would  show  us  a  great  number  of 
minute  pores  which  open  into  tiny 
cavities  or  air  spaces  in  the  interior 
of  the  leaf.  These  pores  furnish  the 
means  of  entrance  for  the  air.  They 
also  provide  an  exit  for  those  constituents  of  the  air  which 
are  not  of  use  to  the  plant,  and  for  the  waste  products  of 


of  a  leaf,  p  is 
opening  into  one  of  the  cells 
below,  fir  is  a  guard  cell; 
two  of  these  regulate  the 
size  of  the  opening  p,  ac- 
cording to  conditions,  ch  is 
one  of  the  few  chlorophyll 
grains  in  guard  cells;  the 
cells  in  the  interior  of  the 
leaf  contain  many  such 
grains.  The  pores  admit 
air  and  give  out  the  water 
vapor  and  oxygen  that  are 
released  by  the  chemical 


living  matter  are  illustrated 

of 


THE    LIFE    OF    A    PLANT  269 

oxidation.  In  the  apple  leaf  there  are  24,000  pores  to  every 
square  inch,  and  in  the  leaf  of  the  black  walnut  there  are 
300,000  to  the  square  inch. 

The  important  work  of  starch  making  in  leaves  will  be 
considered  later  (§302). 

301.  Presence  of  Water  in  Plants.  —  If  seeds  are  placed 
on  damp  blotting  paper,  the  root  hairs  of  the  first  root  will 
turn  downward  to  the  surface  of  the  damp  paper,  even  if  the 
end  of  the  root  does  not  touch  it.     Several  leaves  may  grow 
in  these  conditions;  this  shows  that  water  passes  through  the 
root  hairs  into  the  root,  and  then  up  the  root,  stem,  and 
veins  of  the  leaf,  until  at  last  it  reaches  the  cells  in  the  in- 
terior of  the  leaf. 

Capillarity  and  osmosis  aid  in  this  rise  of  liquids  through 
the  cells  of  the  root  and  the  stem.  Capillarity  makes  the 
liquids  rise  along  the  sides  of  the  slender  tube-like  cells, 
while  osmosis  causes  them  to  pass  from  one  cell  to  the 
next.  Root  pressure  is  the  name  given  to  the  sum  'of  all 
the  agencies  by  which  liquids  are  raised  in  opposition  to 
gravity. 

Water  is  constantly  passing  up  into  the  leaves,  where  a 
large  part  of  it  is  given  off  or  evaporated  through  the  leaf 
pores.  We  can  test  this  fact  by  placing  a  sheet  of  rubber  on 
the  ground  around  a  plant,  and  inverting  a  jar  over  the 
plant.  On  cooling  the  jar,  we  find  that  vapor  condenses  on 
the  inside. 

Experiments  with  sunflower  plants  have  shown  that  a 
single  plant  often  gives  off  a  quart  of  water  a  day,  while  a 
single  birch  tree  with  its  greater  number  of  leaves  may  give 
off  800  quarts  in  the  same  length  of  time.  Grass  may  give 
off  as  much  as  13,000  quarts  per  acre  every  twenty-four 
hours.  (LABORATORY  MANUAL,  Exercise  XXVII.) 

302.  The    Starch-making    Process.  —  Plants,  of  course, 
do  not  elevate  water  simply  for  the  sake  of  evaporating  it 
from  their  leaves.     They  put  water  to  several  important 


270     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

uses.  They  combine  water  chemically  with  carbon  dioxide 
from  the  air  to  form  starch  and  sugar,  which  are  foods  for  the 
growing  plant.  The  starch-making  process  is  carried  on  by 
the  chlorophyll  grains  within  the  interior  cells  of  the  leaf  by 
the  aid  of  the  energy  of  sunlight. 

The  presence  of  starch  in  leaves  may  be  proved.  First 
extract  the  chlorophyll  by  heating  the  leaf  in  alcohol,  until 
the  leaf  has  lost  its  color.  Boil  the  leaf  in  water  to  cook  the 
starch,  and  then  add  a  few  drops  of  iodine.  Iodine  always 
turns  anything  which  contains  cooked  starch  to  a  dark  blue 
color,  and  is  usually  employed  as  a  test  for  the  presence  of 
starch. 

303.  Light  and  Chlorophyll  Necessary  in  Starch  Making. 
It  can  easily  be  shown,  from  leaves  which  have  grown  in 
the  dark,  that  plants  cannot  make  starch  without  light.     Nei- 
ther can  leaves  destitute  of  chlorophyll  make  starch.     Toad- 
stools and  Indian  pipe  have  no  green  color;  the  iodine  test 
shows  no  starch  in  these  plants. 

Starch  making  is  most  rapid  in  direct  sunlight,  but  it 
probably  goes  on  in  all  degrees  of  brightness,  even  in  moon- 
light. Light  from  other  sources  will  also  serve.  For  ex- 
ample, if  an  arc  light  is  in  use  in  a  greenhouse  for  half  of 
every  night,  lettuce  plants  grown  there  will  be  ready  for 
market  a  week  before  others  which  are  not  so  treated.  The 
blooming  of  Easter  lilies  may  in  the  same  way  be  hastened 
from  four  to  ten  days. 

304.  The    Proteid-making    Process.  —  It  may  be  asked 
why  water  is  constantly  carried  up  through  the  plant,  and 
then  in  large  part  evaporated.     It  is  because  the  salts  dis- 
solved in  the  soil  water  are  present  in  such  small  amounts 
that  the  plant  must  absorb  great  quantities  of  water  in  order 
to  secure  enough  of  these  compounds  for  making  proteid. 

These  minerals  are  compounds  containing  several  elements, 
chief  among  which  are  nitrogen,  sulphur,  potassium,  and 
phosphorus.  These  elements  the  plant  combines  with  the 


THE    LIFE    OF    A    PLANT 


271 


elements  of  which  starch  and  sugar  are  composed  —  carbon, 
oxygen,  and  hydrogen  —  to  form  proteid,  another  plant  food. 
Starch  making  can  occur  only  in  green  leaves  and  only  in  the 
light,  but  proteid  making  can  take  place  in  other  parts  of  the 
plant,  and  in  darkness  as  well  as  in  light. 


FIG.  143.— ASA  GRAY:  BOTANIST.     1810-1888 

Very  few  great  investigators  are  willing  to  take  the  trouble  to  prepare 
textbooks  of  their  subject,  much  less  elementary  textbooks.  But  Gray  was 
also  a  great  educator  and  his  ambition  was  to  develop  the  science  of  botany 
by  training  the  greatest  possible  number,  from  the  elementary  schools  to  the 
university.  .  .  .  For  nearly  half  a  century  he  taught  not  only  the  teachers 
but  also  the  children.  —  JOHN  M.  COULTER,  in  Leading  American  Men  of 
Science. 

305.  The  Importance  of  the  Chemical  Work  of  Plants. — 
Plants  themselves  use  these  manufactured  foods  to  build  up 
their  tissues — to  grow,  as  we  say.  If  there  were  an  inex- 
haustible supply  of  carbon  dioxide  in  the  air  and  of  minerals 
in  the  soil,  plants  could  get  along  without  animals.  But  ani- 


272    FIRST   YEAR    COURSE    IN    GENERAL   SCIENCE 

mals  (including  man,  of  course)  could  not  live  a  generation 
without  green  plants,  even  if  there  were  an  abundance  of  all 
the  elements  needed  for  their  growth.  Animals  cannot  make 
organic  matter  from  inorganic  matter. 

Wild  cattle,  horses,  sheep,  and  deer  live  mainly  upon  leaves. 
Domestic  cattle  require  dried  grass  to  eat  in  the  winter. 
Wild  hogs  and  bears  find  their  food  largely  in  nuts  and  roots. 
These  are  simply  a  few  illustrations  of  the  need  of  plants 
among  the  large  herbivorous  animals.  Many  worms,  in- 
sects, and  birds  live  upon  plant  food.  The  waters  of  the 
land  and  of  the  ocean  are  rich  in  plant  life  (some  of  it  micro- 
scopic in  size)  which  is  food  for  fishes,  corals,  and  sponges. 
The  carnivorous  animals  of  the  land  and  sea  feed  upon  the 
herbivorous  animals. 

Starch,  sugar,  fat,  and  proteid  are  the  food  of  all  kinds  of 
animals.  These  are  the  products  of  the  chemical  laboratory 
in  the  plant.  Plants  are  the  food  makers  of  the  world. 

306.  Digestion.  —  Starch  and  proteid  are  foods,  but  both 
of  them  are  insoluble  in  water,  and  hence  need  to  be  digested 
before  they  can  circulate  through  the  plant.     Digestion  con- 
sists in  changing  foods  chemically  so  that  they  are  soluble. 
For  example,   starch  is  changed   to  sugar,   and   then   the 
sugar  is  dissolved  in  the  water  which  is  present  in  every 
part  of  a  growing  plant.     After  this,  the  dissolved  sugar 
can  be  transported  from  the  leaves  to  any  living  cell  of  the 
plant,  to  be  used  as  a  basis  for  making  proteids,  for  immedi- 
ate use  as  food,  or  for  storage  against  future  need. 

307.  Storage  of  Food  in  Plants.  —  Plants  store  food  for 
their  own  use  in  the  root,  as  the  beet  does;  in  the  under- 
ground stem,  as  the  white  potato  does;  or  in  the  base  of 
the  leaves,  as  the  onion  does.     Food  for  the  benefit  of  a 
future  plant  is  always  stored  in  the  seed.     The  reason  that 
roots  of  beets  and  carrots  furnish  food  for  man  and  animal 
is  that  the  plant  has  stored  here  starch,  proteid,  and  sugar 
for  its  own  use  the  next  year,  when  new  stems,  flowers,  and 


THE    LIFE    OF    A    PLANT  273 

seeds  will  grow  from  the  old  root.  The  food  of  man  con- 
sists largely  of  grains,  which  are  rich  in  starch,  stored  for 
the  nourishment  of  the  young  plant  that  would  grow  from 
the  seed.  Man  makes  use  of  materials  which  the  plant 
would  use  if  it  continued  to  live  and  reproduce.  (LABORA- 
TORY MANUAL,  Exercise  XXVIII.) 

308.  Respiration.  —  The  process  of  respiration  for  plants 
is  exactly  the  same  as  for  animals.     It  consists  of  inhaling,  or 
taking  oxygen  into  the  interior  of  the  organism  for  the  pur- 
pose of  oxidation;   and  of  exhaling,  or  expelling  the  gas  re- 
sulting from  oxidation.     The  necessity  of  respiration  for  the 
plant  can  be  easily  shown.     Oxygen  is  necessary  for  the  oxi- 
dation of  foods  and  tissues,  and  for  the  consequent  release 
of  energy  to  be  used  in  movement  and  growth.     Since  plants 
have  a  lower  temperature  and  less  movement  than  many 
animals,  less  oxygen  is  required  to  furnish  energy,  and  less 
carbon  dioxide  and  water  vapor  are  returned  to  the  air. 
When  we  recall  that  starch  and  its  digested  product,  sugar, 
contain  much  carbon  and  hydrogen,  we  can  readily  see  why 
carbon  dioxide  and  water  are  the  substances  resulting  from 
the  oxidation  of  these  foods,  and  why  therefore  they  are 
exhaled. 

309.  Excretion  and  Removal  of  Oxygen.  —  The  term  ex- 
cretion is  commonly  applied  to  the  removal  of  waste  products 
of  oxidation,  such  as  carbon  dioxide  and  water,  which  are 
eliminated  because  they  are  of  no  further  use  in  the  cells  of 
the  plant. 

In  the  making  of  protoplasm,  proteid  food  is  chiefly  used. 
If  it  is  oxidized,  as  is  sometimes  the  case,  it  forms  products 
not  easily  excreted,  because  they  cannot  be  given  off  as  gases, 
as  can  water  and  carbon  dioxide.  So  these  waste  products, 
together  with  certain  salts  from  the  soil,  which  perhaps  can- 
not be  .utilized,  become  stored  in  leaves,  bark,  and  fruit.  As 
these  parts  are  in  time  detached,  the  waste  products  from 
proteid  are  removed  from  the  plant. 


274     FIRST   YEAR   COURSE    IN    GENERAL    SCIENCE 

Another  very  important  work  of  plants  is  the  giving  off 
of  oxygen  from  the  carbon  dioxide  which  the  plant  absorbs 
from  the  air.  The  carbon  only  is  used  in  starch  making, 
and  the  oxygen  is  passed  out  through  pores  in  the  leaves. 
As  starch  making  occurs  naturally  only  in  sunlight,  so  the 
liberation  of  oxygen  occurs  only  in  the  daytime.  Oxygen  is 
not  a  waste  product  but  a  residue  that  is  useless  to  the 
plant. 

310.  The  Processes  of  Plant  Nutrition.  —  Plant  nutri- 
tion includes  : 

The  preparation  of  food  from  materials  in  soil,  water,  and 
air. 

The  digestion  of  these  foods. 

The  excretion  of  waste  products  of  oxidation. 

The  use  of  the  foods  in  individual  cells,  either  to  make  new 
protoplasm  in  the  process  of  growth  and  repair,  or  to  yield 
energy  through  oxidation  by  means  of  the  oxygen  taken  from 
the  air. 

The  elimination  of  any  useless  residue. 

EXERCISES 

1.  Why  do  we  not  usually  see  the  root  hairs  when  a  plant  is 
dug  up? 

2.  (a)  Why  does  the  gardener  take  pains  to  keep  soil  about  the  roots 
of  a  plant  which  he  is  transplanting?     (6)  What  is  the  effect  on  a  plant 
if  the  soil  is  dry?     (c)  Explain  the  change  that  watering  produces. 

3.  (a)  In  what  state  is  the  water  given  off  from  leaves  of  plants? 
(6)  Describe  a  simple  method  by  which  we  could  show  that  it  is  given 
off. 

4.  How  can  carbon  dioxide  reach  the  interior  of  a  leaf? 
6.   What  substances  pass  out  of  the  pores  of  a  leaf? 

6.  What  would  be  the  appearance  of  a  leaf  after  the  chlorophyll 
had  been  removed? 

7.  Name  some  plants  having  simple  leaves;    others  (besides  the 
bean)  having  compound  leaves. 

8.  What  organs  of  a  plant  are  its  starch  factories? 

9.  How  do  the  materials  used  there  get  to  these  organs? 


THE    LIFE    OF    A    PLANT  275 

10.  From  what  materials  do  plants  prepare  food? 

11.  (a)  What  is  prepared  from  starch  by  digestion?      (6)  For  what 
is  the  product  used? 

12.  What  waste  products  do  plants  excrete? 

13.  What  materials  useless  to  the  plant  are  otherwise  eliminated? 


CHAPTER  XXIV 
REPRODUCTION  AND   DEVELOPMENT   OF  PLANTS 

311.  The  Object   of  Reproduction.  —  Up  to  this  point 
only  the  activities  necessary  to  the  plant  itself  have  been 
considered.    A  maple  tree  three  feet  high,  or  a  wheat  plant 
six  inches  above  the  ground,  is  a  complete,  independent 
plant.     It  responds  to  the  influence  of  water  and  light;   it 
makes  its  own  food;  that  food  is  digested  and  new  cells  are 
formed  from  the  product.     Oxidation  of  parts  of  the  plant 
gives  heat  and  energy  for  necessary  movements.    If,  however, 
the  plant  died  at  this  stage,  its  death  would  be  premature. 
It  would  have  failed  to  provide  for  the  continuance  of  its  own 
race.     The  function  of  reproduction,  without  which  a  race 
of  plants  or  animals  ceases,  is  performed  only  by  a  mature 
organism. 

312.  The  Structure  of  Flowers.  —  Many  plants,  of  which 
the  bean  plant  is  a  type,  reproduce  by  means  of  seeds  found 
in  the  pod  after  the  flower  withers.     Therefore,  in  the  study 
of  reproduction  it  is  convenient  to  begin  with  the  flower. 
Flowers  differ  greatly  in  color,  size,  and  shape;   but  if  com- 
plete, they  all  have  petals,  sepals,  stamens,  and  one  or  more 
pistils.     The  simplest  flowers  have  these  parts  quite  separate; 
but  some  flowers,  such  as  the  bean,  show  some  of  these  parts 
united. 

The  garden  bean  plant  has  five  petals,  usually  white,  two 
rather  closely  placed  petals  being  below  the  other  three.  On 
the  back  or  under  side  of  the  flower  there  are  five  green  sepals, 
partially  united.  The  flower  has  also  ten  yellow  stamens 
and  a  single  pistil.  The  knobs,  called  anthers,  at  the  ends 
of  the  stamens  are  really  hollow  sacs  producing  a  large 

276 


REPRODUCTION   AND    DEVELOPMENT    OF    PLANTS     277 


number  of  fine  yellow  grains,  called  pollen.  The  rather  stout 
basal  part  of  the  pistil,  called  the  ovary,  contains  small  white 
rounded  bodies,  called  ovules.  The  beans  are  fastened  at 
the  sides  of  the  ovary;  some  seeds  are  fastened  at  the  mid- 
dle. The  bean  pod  shows  the  place  of  attachment  very 
plainly.  (LABORATORY  MANUAL,  Exercise  XXIX.) 

313.  Pollination.  —  The  pollen  from  the  stamens  is  trans- 
ferred to  the  tip  of  the  pistil  by  some  agency,  such  as  gravity, 
insects,  birds,  or  wind.  This  process  is  termed  pollination. 
Small  birds  searching 
for  insects,  and  insects 
looking  for  food,  thrust 
their  heads  or  even  their 
entire  bodies  into  a 
flower  and  rub  the  pol- 


Anther 
Filament 


Stigma 


Petal 


FIG.  144.  —  FLOWER 

1.  The  ovary  of  this  flower  contains 
only  one  ovule.  How  is  it  kept  in  place? 
2.  How  can  you  tell  whether  this  is  a  cherry 


len  from  the  stamens 
upon  their  bodies.  As 
they  withdraw,  they 
sometimes  leave  some 
pollen  upon  the  stigma,  ?r  an  aPple  bl°ssom?  3flwhat9 

^  r  inside   the    anthers  of  a  flower?     4.  What 

which  is  the  top  of  the     is    the    most    common    color    in    anthers? 

pistil;  but   more  often    5- w,hat   rfason   can   ^   give   for  the 

pistil  s  position  in  a  flower? 

they  carry  it  to  the  next 

flower  and,  entering,  scatter  it  upon  the  stigma,  thus  securing 

pollination  for  that  flower.  . 

314.  Fertilization.  —  Microscopic  study  of  an  ovule  shows 
it  to  be  composed  of  cells,  one  of  which  is  called  the  egg  cell. 
The  pollen  grain  contains  a  special  cell  called  the  sperm  cell. 
When  a  pollen  grain  is  left  on  the  tip  of  the  pistil,  a  long 
delicate  tube  grows  from  the  pollen  grain  down  through  the 
pistil  till  it  comes  to  an  ovule.  It  pierces  the  ovule  and  thus 
reaches  the  egg  cell.  Through  this  tube  the  sperm  cell  of 
the  pollen  grain  travels,  till  it  reaches  the  end  of  the  tube 
and  meets  the  egg  cell.  The  two  cells,  coming  together, 
unite  and  form  a  single  cell.  This  union  of  egg  cell  and  sperm 


278     FIRST   YEAR    COURSE    IN    GENERAL    SCIENCE 

cell,  to  form  a  fertilized  egg  cell,  is  known  as  fertilization. 
Pollination  may  occur  without  resulting  in  fertilization,  but 
fertilization  never  occurs  without  previous  pollination. 

315.  The  Result  of  Fertilization.  — -Soon  the  fertilized  egg 
cell  divides  to  form  two  cells  and,  after  growth,  these  new 
cells  divide.     This  process  of  cell  division  is  repeated  until 
an  embryo,  or  baby  plant,  is  formed  within  the  ovule.     At 

the  same  time,  food  is  being 
furnished  by  the  plant  which 
bore  the  flower  and  is  stored  in 
the  ovule  for  the  nourishment 
of  the  young  plant.  The  ovule 
is  now  known  as  a  seed. 

While  the  ovules  in  a  bean 
flower  are  developing  into  seeds, 
the  ovary  elongates  and  becomes 
FIG.  145.  — BUMBLE-BEE  GOING    the    pod.       Long    before    this, 
INTO  A  FLOWER  tne  petals  and  stamens   have 

Describe  the  way  in  which    withered  away  and    later  the 

ofethisefltwerUt  "  P°"inati0n    sepals  also,  until  now  nothing 

remains  but  the   fruit,    which 

consists  of  the  ovary  and  the  seeds.  When  the  fruit  is  ripe, 
the  seeds  easily  become  detached  and  drop  out  of  the  dry  pod. 
Examination  of  a  bean  seed  shows  on  one  edge  an  oval- 
shaped  scar  made  by  its  connection  with  the  ovary. 

316.  Structure   of   the   Bean  Seed.  — The   seed   coat  is 
easily  stripped  from  a  bean  soaked  in  water  over  night.     The 
body  within,  called  the  embryo,  is  seen  to  consist  of  two 
thickened  halves,  seed-leaves,  filled  with  proteid  and  starchy 
food.     They  could  be  tested  for  the  starch  by  means  of 
iodine.     The  presence  of  proteid  in  the  seed  may  be  shown 
by  the  orange  color  given  to  it  on  adding  a  drop  of  nitric 
acid,  followed  by  ammonia. 

A  short,  stubby,  rod-like  body  is  joined  to  the  two  seed- 
leaves.     From  its  free  pointed  end  grows  the  root,  and  the 


REPRODUCTION    AND    DEVELOPMENT    OF    PLANTS     279 


part  next  to  the  seed-leaves  becomes  the  stem.  Upon  care- 
fully separating  the  two  -seed-leaves,  there  is  found  a 
pair  of  small  thin  leaves,  with  a  bud  between  them, 
attached  to  a  very  short  stem,  which  is  joined  to  the  stem 
part  of  the  rod-like  body.  (LABORATORY  MANUAL,  Exercise 
XXX.) 

317.  Process  of  Germination.  —  To  see  what  becomes  of 
the  parts  of  the  embryo,  let  us  plant  a  bean  seed.  If  the  seed 
is  put  in  a  warm,  moist  place,  where  there  is  air,  it  will  soak 
up  water  and 
swell,  and  pres- 


ently the  embryo 
or  baby  plant  in- 
side, which   has 
been  dormant  while  the  seed  was 
dry,   will    continue    its   growth, 
c 


_a 


FIG.  146. —  THE  BEAN 
EMBRYO 

1.  What  are  the  names  of 
the  parts  a?  What  will  grow 
from  d?  2.  How  do  you  know 
that  c  will  grow  to  be  a  stem? 
3.  What  becomes  of  the  two  large 
parts  of  the  embryo? 


C 


FIG.  147. —  SEED  PODS 

The  bean  pod  represents  a 
lengthwise  section  of  an  ovary; 
the  triangular  figure  represents  a 
cross-section  of  the  ovary  of  a 
lily.  In  both  cases,'  a  represents 
the  wall  of  the  ovary;  b  represents 
an  ovule.  1 .  Where  are  the  ovules 
attached  in  the  bean  pod?  Where 
are  they  attached  in  the  lily  pod? 
2.  How  many  divisions  are  there 
in  the  lily  pod?  How  many  in 
the  bean  pod? 


This  " awakening"  and  growth  into  an  independent  plant  is 
called  germination,  and  the  seed  is  said  to  germinate. 


280     FIRST    YEAR    COURSE    IN    GENERAL    SCIENCE 


318.  The  Result  of  Germination.  —  The  embryo  bursts 
open  the  seed  coats,  and  as  the  seed-leaves  absorb  moisture 
from  the  soil,  a  chemical  change  takes  place  in  the  starch  and 
proteid  stored  in  the  seed-leaves.  They  become  soluble 
and  furnish  food  and  energy  for  the  young  plant  to  live  on 
until  it  has  a  root  capable  of  taking  water  from  the  ground, 
and  leaves  to  take  carbon  dioxide  from  the  air.  When  it 
can  make  its  own  food  in  this  way,  the  seedling  has  become 
"self-supporting."  In  time  it  will  become  a  mature  plant 


--d 


FIG.  148.  —  BEAN,  PEA,  AND  CORN  SEEDLINGS 

1.  Give  the  name  of  the  organ  designated  by  each  letter  in  the  picture 
of  the  bean.  2.  What  difference  is  there  in  the  position  of  the  correspond- 
ing organs  in  the  pea?  3.  What  differences  are  there  between  the  corn 
seedling  and  both  of  the  others?  4.  What  peculiarity  of  the  corn  seedling 
is  explained  by  the  fact  that  from  10  to  20  tons  of  water  are  required  to 
raise  a  bushel  of  corn? 

having  flowers,  fruit,  and  seed  of  its  own.  Thus  the  family 
of  bean  plants  is  continued  by  the  process  of  reproduction. 
319.  Flowerless  Plants.  —  There  are  some  plants  which 
do  not  have  flowers  containing  reproductive  organs.  In 
such  plants  the  function  of  reproduction  is  accomplished  in 
one  of  two  ways.  In  some  of  the  simplest  microscopic  forms 


REPRODUCTION    AND    DEVELOPMENT    OF    PLANTS     281 

of  plants,  there  are  no  organs  of  any  kind.  A  single  cell  is  the 
whole  plant.  Reproduction  takes  place  when  the  cell  sepa- 
rates into  two  cells,  thus  forming  two  plants.  In  higher 
flowerless  plants,  spores  are  produced  and  from  these 
bodies  new  plants  grow.  Spores  are  very  small  bodies 
which  look  like  dust.  They  do  not  have  an  embryo  —  a 
complete,  minute  plant  within  the  covering — as  a  seed  does, 


FERN  GROUND  PINE  MUSHROOM 

FIG.  149.  —  THREE  FLOWERLESS  PLANTS 

The  letter  a  indicates  the  part  of  the  plant  which  bears  the  spores. 
The  mushroom  is  never  green.  What  does  that  imply  in  regard  to  its  food 
making? 

but  contain  only  a  minute  portion  of  protoplasm.  Ferns, 
club-mosses,  and  puff  balls,  when  dry,  discharge  thousands 
of  spores  on  being  shaken. 

Some  flowerless  plants  find  food  material  in  the  leaves  and 
fruit  of  other  plants,  as  do  molds  and  yeast;  and  some  in 
decaying  organisms  in  the  soil,  as  the  mushroom;  ferns  and 
mosses,  however,  usually  require  soil  for  development. 
Mosses  and  ferns  have  chlorophyll  in  their  leaves;  mush- 
rooms, yeast,  and  bacteria  have  none. 

There  are  some  plants,  like  palms  and  rubber  plants,  which 


282     FIRST   YEAR    COURSE    IN    GENERAL    SCIENCE 

do  not  blossom  under  the  artificial  conditions  in  which  they 
are  grown.     These  should  not  be  called  flowerless  plants. 

320.  The     Influence     of     Light.  —  One  of  the  most  re- 
markable things  about  protoplasm  is  its  sensitiveness  to  its 
surroundings  and  its  power  to  respond  in  certain  definite 
ways  to  varying  outside  conditions.     For  example,  proto- 
plasm is  stimulated  or  roused  to  activity  by  light.     If  a  bean 
plant  is  grown  in  the  dark,  the  stem  will  increase  in  length 
more  quickly  than  usual,  but  the  leaves  will  be  small  and  will 
lack  the  usual  green  color.     If  a  ray  of  light  is  admitted  into 
the  dark. place,  the  stem  will  immediately  grow  toward  this 
light.     The  stems  of  house  plants,  which  receive  a  compara- 
tively small  amount  of  light  from  windows,  are  more  slender 
and  paler  than  the  stems  of  those  grown  out-of-doors  and 
not  shaded  by  neighboring  plants.     Moreover,  plants  grown 
indoors  always  turn  in  one  direction  —  toward  the  light. 

321.  Growth    Movements.  —  Only  the  younger,  growing 
parts  of  plants  move  under  the  influence  of  light,  as  it  is 
difficult  for  the  older  and  somewhat  rigid  parts  to  change 
their  position.     This  response  by  movement  is  brought  about 
by  the  more  rapid  growth  of  the  stem  on  one  side  than  on  the 
other.     When  the  bean  plant  is  unequally  lighted,  growth  is 
most  rapid  on  the  side  away  from  the  brightest  light,  and 
this  makes  the  top  curve  toward  the  light. 

322.  —  Another    Response    to    Light.  —  The  behavior  of 
the  tips  of  young  shoots  of  English  and  Japanese  ivies,  which 
are  often  seen  covering  the  walls  of  stone  or  brick  build- 
ings, is  quite  the  reverse  of  that  of  the  bean  plant.     They 
turn    away  from    the  light,    though    the    leaves  still  face 
the  light.     The  ivies  hold  themselves  in  position  by  short 
root-like  growths  on  the  stems,  which  attach   themselves 
to  the  rough  stone.     If  the  tip  of  the  stem  turned  toward 
the   light,  the  hold   of  the  vine  on   the    stone  would    be 
weakened.     Different  parts  of  the  plant  thus  make  differ- 
ent responses  to  the  stimulus  of  the  light. 


REPRODUCTION    AND    DEVELOPMENT    OF    PLANTS     283 


FIG.    150.— POTATO    SPROUTS 
GROWN  IN  A  CELLAR 

This   picture  illustrates  the 
fact  that  a  potato  is  an  under- 
ye"  of  the 
bud  which 


323.  The  Behavior  of  Flowers.  —  Certain  flowers,  such  as 
the  crocus  and  dandelion,  open  in  the  light  and  close  in  the 
dark,  whether  it  be  at  night  or  in  cloudy  weather.     This 
makes  them  ready  to  admit  by  day  insect  visitors,  which 
in  their  search  for  nectar  receive  pollen  on  their  bodies  to 
be  carried  to  other  flowers.     It  also  enables  the  flowers  to 
protect  their  pollen  from  dew  by 

night  or  from  possible  rain  on  a 
cloudy  day. 

324.  Motor     Organs. —  The 
old  parts  of  some  plants,  being 
too   rigid   to   move    easily,    are 
usually    provided    with    special 
structures  to  produce  movement. 
Examination  of  the  base  of  the 
leaf  stalk  of  the  bean,  and  also  of 

the  tiny  stalks  of  the  separate  will  develop  into  a  branch  bear- 
leaflets,  will  show  slight  enlarge-  ^  ^und. ^i.  rromTh^ch^de 
ments,  which  are  called  motor  does  the  light  come?  How  do 
organs.  These  organs  are  com- 
posed of  cells  containing  much 
water.  Variations  in  the  inten- 
sity of  light  to  which  the  bean 
plant  is  exposed  will  cause  rather  prompt  changes  in  the 
amount  of  water  in  the  cells  of  one  part  or  another  of  the 
motor  organs.  In  the  dark,  the  cells  of  the  upper  part  of 
the  motor  organs  of  the  leaflets  become  full  of  water  and  so 
the  leaflets  are  made  to  droop.  In  the  light,  the  reverse 
conditions  occur. 

325.  Change     of    Response.  —  The  kind  of  response  to 
light  stimulus  may  change  at  different  stages  of  development 
and  growth.     The  flower  stalks  of  a  certain  plant  turn  to- 
ward the  light  when  the  buds  first  open  and  remain  so  until 
after  the  pollination  by  insect  visitors.     Then,  as  they  grow 
longer,  the  stalks  turn  away  from  the  light,  and  push  their 


Men  cut  a  potato  into  pieces  be- 
fore planting.  Will  every  part  of 
a  potato  make  a  branch?  Why? 


284     FIRST   YEAR   COURSE    IN    GENERAL   SCIENCE 


seeds  into  the  crevices  of  the  rock  on  which  the  plant  grows. 
The  flower  of  the  peanut  plant  opens  and  is  pollinated  in 
the  light,  but  after  pollination  its  stalk  turns  downward  and 
pushes  the  young  seed  pod  into  the  ground,  where  it  ripens. 
Although  peanuts  are  pulled  from  the  ground,  they  are  not 
roots  nor  stems,  but  ripened  ovaries  and  seeds. 

326.  The  Influence  of  Gravity.  —  We  are  not  surprised 
to  learn  that  plants  make  use  of  a  constant  and  universal 
force  such  as  gravity  in  guiding  their 
organs  into  suitable  positions.  The 
fact  that  roots  grow  downward  is  so 
familiar  that  we  do  not  usually  think 
of  it  as  needing  explanation.  No 
matter  in  what  position  a  bean  seed 
is  planted,  the  primary  root  will  grow 
down  and  the  stem  up.  We  could 
demonstrate  that  the  direction  of 
growth  is  determined  by  gravity  if  we 
could  study  a  plant  in  some  region 
where  gravity  did  not  exist.  This,  of 
course,  cannot  be  done;  but  we  can 
These  beans  were  all  place  several  germinated  seeds  with 
the  root  tips  pointing  in  different  di- 


FIG.   151.  — THE  INFLU- 
ENCE OF  GRAVITY 


sprouted  under   the   same 
conditions  and  were 

placed,  when  the  sprouts    rections  and  watch  their  growth. 

were  very  short,    between          -p,        -,          .  r         ,1  i    ,,• 

moist  blotting   paper   and          Be™  a  Piece  ot  wet  blotting  paper 

glass,     i.    Describe    the    to  fit  the  inside  of  a  tumbler  like  a 

change     of     direction     in     r    •  ™  , 

some  of  the  sprouts.  2.  in  hning.  Place  several  germinated 
which  cases  has  there  been  beans  or  peas  between  the  paper  and 

no    change    of    direction?     ,v         i  •,-,     .-,  .    .. 

3.    What  conclusion  in  re-     tne  Slass>  One  Wlth  the  root  Pointing 

gard  to  the  influence  of    up,  one  to  the  right,  one  to  the  left, 

gravity    could    be    drawn  -,  -,          i     -i          •       T™» 

from  these  two  answers?       one  downward,  and  others  in  different 
directions.     After  a  few  days  every 

tip  will  point  downward,  some  roots  having  made  a  short 
turn,  and  some  having  wound  around  the  seed  before  it 
was  possible  to  turn  downward. 


REPRODUCTION    AND    DEVELOPMENT    OF    PLANTS      285 

Experiments  on  bean  seedlings  placed  in  a  horizontal  posi- 
tion in  the  dark  show  that  the  stems  turn  and  grow  upward, 
while  the  primary  root  turns  and  grows  downward.  This 
shows  that  it  is  gravity  and  not  light  which  gives  direction 
to  the  growth  of  stems. 

Some  parts  of  plants  may  respond  to  gravity  by  growing 
in  a  horizontal  direction  or  at'  any  intermediate  angle,  as  is 
shown  by  the  branches  of  the  main  stem  and  by  secondary 
roots.  Thus  gravity  seems  to  act  as  a  pointer  or  directive 
force,  so  to  speak.  More  rapid  growth  on  one  side  of  the 
stem  or  branch  is  the  power  that  sends  that  part  of  the 
plant  into  the  required  position. 

327.  The  Influence  of  Water.  —  Whenever  any  external 
force  or  substance  is  important  to  the  life  of  a  plant  organ, 
the  organ  develops  a  corresponding  sensibility  to  the  influ- 
ence of  that  force  or  substance.     Thus  roots  respond  to 
water.     If  water  is  evenly  distributed,  roots  develop  equally 
on  all  sides;    otherwise  roots  grow  only  in  the  direction  of 
greatest  moisture.     An  example  is  found  in  the  fact  that 
roots  of  trees  often  enter  and  block  up  tile  drains  laid  in  wet 
ground,  long  distances  from  the  tree  itself. 

In  watering  house  plants,  water  should  be  placed  in  a 
saucer  under  the  pot  rather  than  on  the  surface.  The  roots 
turn  toward  the  water,  and  if  that  brings  them  near 
the  surface,  they  are  more  likely  to  become  dry  between 
waterings. 

328.  The    Influence    of    Contact.  —  Irritability  of  proto- 
plasm    to    contact     with    objects     is    almost    universal. 
Tendril  climbers,  such  as  the  pea,  a  near  relative  of  the 
bean,   make  use  of   this  irritability  with  the  result  that 
they  attach  themselves  to  supports.     In  this  way  they  are 
enabled  to  elevate  their  leaves  and  flowers  into  more  favor- 
able situations.     When  the  tendril  touches  the  solid  body, 
growth  on  that  side  is  stopped,  while  growth  on  the  opposite 
side  is  increased  and  the  tendril  curves. 


286     FIRST    YEAR    COURSE    IN    GENERAL    SCIENCE 

The  folding  together,  when  touched,  of  the  leaflets  of  the 
sensitive  plant  is  brought  about  by  differences  in  amount  of 
water  in  the  cells  of  the  motor  organs.  Contact  or  even  a 
sudden  jar  of  the  plant  is  a  stimulus  to  which  protoplasm 
responds  by  regulating  the  water  in  the  motor  organs.  The 
closed  leaf  has  a  smaller  surface  exposed  to  the  wind  or  to 
voracious  enemies. 

It  is  thus  seen  that  responses  are  made  by  the  plants  them- 
selves, the  external  influence  or  force  acting  simply  as  a  signal 


FIG.  152.  —  LEAF  OF  A  SENSITIVE  PLANT 

1.  Measure  in  mm.  the  length  and  width  of  one  of  the  leaflets  in  the 
open  leaf  and  give  an  estimate  of  the  area.  2.  Give  the  total  area  of  the 
leaflets  of  one  division  of  the  four-parted  leaf.  3.  Compare  it  with 
the  exposed  surface  of  one  of  the  divisions  of  the  closed  leaf.  4.  What  would 
be  the  advantage  of  the  closed  leaf  in  regard  to  heat,  air,  or  plant  enemies? 

or  stimulus.  The  result  is  the  bringing  of  organs  into  better 
positions  for  doing  their  work  or  for  protecting  themselves 
from  injury. 

329.  Internal  Cause  of  Movement  in  Plants.  —  The 
movements  of  plants  so  far  studied  are  brought  about  or 
guided  by  some  external  force,  although  in  all  cases  the  living 
protoplasm  causes  the  useful  movement.  There  is,  however, 
another  class  of  movements  which  do  not  appear  to  result 
from  external  conditions,  and  are  hence  thought  to  be  due  to 
some  internal  cause — although  just  what  this  cause  is  has 
not  yet  been  determined. 


REPRODUCTION  AND  DEVELOPMENT  OF  PLANTS  287 

Under  the  microscope  the  protoplasm  in  cells  is  seen  to  be 
constantly  flowing  around  inside  the  cell  wall.  The  growing 
tips  of  roots  and  stems  are  almost  constantly  in  motion. 
These  movements  are  usually  very  slight,  though  one 
example  may  be  quoted  to  show  that  they  are  sometimes 
easily  seen.  On  the  banks  of  the  Ganges  River  there  grows 
a  plant  related  to  the  bean,  the  tips  of  whose  leaves  make 
constant  movements  in  the  air,  so  that  they  describe  a  com- 
plete circle  in  less  than  three  minutes. 

330.  The  Sun,  the  Source  of  Energy  for  Life  Processes. 
How  the  living  protoplasm  is  able  to  carry  out  the  life 
processes  of  nutrition,  reproduction,  irritability,  and  spon- 
taneous motion  is  a  mystery.  We  know  in  regard  to 
it,  however,  that  the  protoplasm  ceases  its  activity 
and  dies  unless  a  certain  amount  of  internal  energy  is 
available. 

This  energy,  in  the  form  of  heat,  is  derived  from  oxidation 
of  the  protoplasm  itself  and  of  food  material  not  needed  for 
growth  and  reproduction.  No  amount  of  energy  supplied 
externally  can  take  'the  place  of  the  necessary  internal 
energy.  If  growth  and  movement  are  rapid,  more  energy 
is  required  —  and  therefore  a  greater  amount  of  material  is 
consumed  — than  if  movement  is  sluggish  or  growth  slow. 

The  sun  is  the  main  source  of  energy  for  living  bodies. 
The  internal  energy,  heat,  set  free  during  respiration  is 
obtained  from  the  oxidation  of  tissues  made  from  food. 
This  food  is  largely  starch,  —  made  only  under  the  in- 
fluence of  light,  —  and  proteid  made  from  starch  and  from 
salts  taken  from  the  soil.  When  the  tissues  of  the  body  are 
broken  up  or  decomposed  in  the  process  of  oxidation,  this 
energy  is  set  free  and  is  used  by  the  plant.  Thus  it  ap- 
pears that  the  most  important  thing  about  food  making  is 
that  it  is  a  process  of  storing  up  the  sun's  energy  by  the 
plant,  just  as  the  coal  making  of  the  past  stored  energy  for 
present  use.  The  plant  requires  energy  by  night  as  well  as 


288     FIRST   YEAR    COURSE    IN    GENERAL    SCIENCE 

by  day,  and  throughout  all  seasons;    so  in  the  sunshine  it 
stores  energy  for  future  need. 

EXERCISES 

1.  What  is  the  reason  that  the  petals  of  a  flower  are  generally 
showy? 

2.  Of  what  use  to  a  flower  is  its  odor? 

3.  What  two  parts  of  the  flower  do  you  consider  most  important? 
Why? 

4.  Why  do  not  snowdrops  and  lilies  of  the  valley  open  and  close 
their  flowers  as  tulips  do? 

6.    (a)  How  could  you  show  that  starch  was  present  in  the  seed- 
leaves  of  an  embryo?     (b)  For  what  purpose  is  food  stored  in  a  seed? 

6.  (a)  How  is  sensitiveness  to  the  stimulus  of  contact  of  use  to 
a  nasturtium?     (6)  To  a  grape  vine? 

7.  The  beet  and  the  turnip  are  two  of  the  plants  that  do  not  blos- 
som until  the  second  summer  after  a  seed  is  planted.     What  relation 
is  there  between  this  fact  and  the  fact  that  they  have  thick  roots? 

8.  Explain  how  a  plant  can  grow  and  blossom  from  a  bulb  put 
into  water  only. 

9.  What  does  a  plant  gain  by  its  response  to  the  influence  of  light? 

10.  Of  what  advantage  to  a  plant  is  the  folding  of  its  leaves  at  night? 

11.  Name  all  the  steps  in  tracing  man's  energy  back  to  the  heat  of 
the  sun. 


CHAPTER  XXV 
THE  LIFE  OF  AN  ANIMAL 

331.  Simple  and  Complex  Organisms.  —  When  we  speak 
of  organisms  as  lower  and  higher,  simple  and  complex,  we  refer 
to  the  structure  of  the  body.  The  simplest  organisms  con- 
sist of  one  cell,  microscopic  in  size,  and  averaging  about 


FIG.  153.  —  ONE-CELLED  ANIMALS,     (magnified) 

These  minute  animals  live  in  stagnant  fresh  water.  Their  food  con- 
sists of  microscopic  plants  and  animals.  The  globular  part  of  C  consists 
of  grains  of  sand  which  the  animal  gathers  upon  its  surface  for  protection. 

sinnr  of  an  inch  in  diameter.  Such  bodies  possess  no  organs. 
Food  is  absorbed  in  liquid  form  at  any  part  of  the  cell.  Re- 
production takes  place  by  increase  in  the  size  of  the  cell, 
followed  by  separation  into  two  cells.  These  simple  organ- 
isms have  all  the  physiological  properties  of  protoplasm, 
which  is  their  sole  constituent.  They  are  themselves  food 
for  organisms  slightly  more  complex,  which  perhaps  have 
one  opening  that  serves  both  to  receive  food  and  "to  reject 
the  insoluble  residue,  and  a  central  cavity  where  digestion 
takes  place. 

289 


290      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

For  the  most  part  we  are  ignorant  of  these  simple  organ- 
isms, because  we  can  neither  see  them  nor  taste  them.  They 
exist  even  in  drinking  water,  on  the  surface  of  fruits,  in  the 
air  we  breathe.  Some  are  plants  and  some  are  animals,  and 
these  two  classes  sometimes  have  so  close  a  resemblance 
that  it  is  difficult  for  those  who  have  not  studied  them 
very  minutely  to  determine  "  which  is  which." 

The  one-celled  animal  in  its  general  daily  life  performs  all 
the  functions  which  the  higher  and  more  complex  animals 
perform.  That  is,  the  one  cell  carries  on  the  many  processes 
which  in  the  higher  animal  are  divided  among  various  organs. 

As  we  go  somewhat  higher  in  the  scale,  we  find  such  ani- 
mals as  worms,  oysters,  snails,  lobsters,  and  insects,  which 
are  more  complex.  They  have  special  organs  adapted  to  the 
functions  of  motion,  nutrition,  and  reproduction. 

The  highest  group  of  all,  the  vertebrates,  or  back-boned 
animals,  is  the  one  to  which  fishes,  reptiles,  birds,  and  the 
familiar  domestic  animals  belong.  Man  is  the  highest  type 
of  the  vertebrates. 

332.  The    Nervous    System.  —  In  the  simplest  animals, 
irritability  does  not  belong  to  any  particular  part  of  the 
body,  but  is  possessed  equally  by  all  the  protoplasm.     But  in 
the  higher,  many-celled  animals,  only  special  groups  of  cells 
respond  to  external  conditions.     These  groups  are  set  apart 
to  take  charge  of  the  relation  of  the  animal  to  its  surroundings, 
and  of  the  relation  of  one  part  of  the  animal  to  other  parts. 
They  perform  no  other  work.     Some  groups  of  cells  direct 
the  organs  of  motion;  some  groups  control  the  work  of  nu- 
trition;   others  are  concerned  with  sensation  and,  in  the 
higher  animals,  with  thinking,  remembering,  willing,  and  the 
like.     All  these  groups  taken  together  constitute  the  nervous 
system. 

333.  The    Divisions    of    the    Nervous    System.  —  The 
nervous    system    consists   of    three    divisions:     the    sense 
organs,  the  nerves,  and  the  nerve  centers.     Each  of  these 


THE    LIFE    OF   AN    ANIMAL 


291 


parts  is  composed  of  groups  of  cells.     A  nerve  cell  consists 

usually  of  an  angular  body  with  thread-like  branches.     It 

has  one  very  long  outgrowth,  called  an  axon.     Thousands 

of  nerve  cells  grouped  together  make  a 

nerve  center,  and   the    axons   of    these 

cells  form  bundles  of  nerve  fibers  called 

nerves.     Each  fiber  is   protected  by  a 

covering  or  sheath.      The  nerves  serve 

to  connect   the   nerve  centers   with  the 

sense  organs,  muscles,  and  other  active 

organs  of  the  body. 

334.  Sense   Organs.  —  Some  cells  of 
the  nervous  system  are  highly  sensitive 
to  external  changes,  and  are  found  on  or 
near  the  surface  of  the  body.     These  con- 
stitute sense  organs.     The  eye  is  a  sense 

organ.     In  the  tips  of  the  fingers  there          The    thread-like 

orp  <,pn«P  ore-arm  projection    from    the 

0rSans-  main  body  of  the  cell 

335.  Nerves.  —  There  are  two  classes   is  one  of  the  fibers 
of   nerves:  sensory   and    motor   nerves. 

The  sensory  nerves  are  so  arranged  in 
the  body  as  to  form  a  connection  between  the  sense  organs 
and  the  nerve  centers,  such  as  the  brain  and  the  spinal  cord. 
The  motor  nerves  connect  nerve  centers  with  the  different 
organs  of  the  body.  Both  kinds  of  nerves  are  found  in  all 
parts  of  the  body. 

A  sensory  nerve  carries  inward,  to  a  nerve  center  from 
some  sense  organ,  an  impulse  caused  by  an  external  change 
or  stimulus.  Motor  nerves  carry  outward,  from  a  nerve 
center,  answering  impulses  to  different  organs.  Because 
motion  so  often  results  from  these  answering  impulses,  the 
nerves  which  carry  them  are  called  motor  nerves. 

Illustration:  a  footfall  jars  the  ground  near  a  toad.  The 
vibration  of  the  ground  arouses  or  gives  stimulus  to  sensory 
nerves  in  the  toad,  which  convey  the  information  as  an 


154.— 
A  NERVE  CELL. 
(magnified) 


of  thread-like  sensory 
and  motor  nerves. 


292      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

impulse  to  a  nerve  center.  The  nerve  center  sends  another 
impulse  through  a  motor  nerve  to  a  group  of  muscles,  and 
the  toad  jumps.  These  impulses  are  conveyed  so  rapidly 
that  before  the  foot  which  caused  the  stimulus  is  lifted,  the 
toad  is  a  yard  away. 

336.  Nerve   Centers.  —  Nerve  centers  are  groups  of  cells. 
They  receive  impulses  brought  to  them  over  sensory  nerves, 
and  they  send  out  answering  impulses  over  motor  nerves. 
The  brain  and  spinal  cord  are  nerve  centers.     The  brain  may 
be  compared  to  an  operator  in  a  telephone  exchange;  it 
receives  calls  from  a  distant  part  of  the  body  and  connects 
with  a  muscle  which,  on  contracting,  moves  an  organ  in 
response  to  the  return  message. 

337.  The   Importance    of   the    Nervous    System.  —  The 
nervous  system  is  of  great  importance,  since  it  provides  for 
the  harmonious  working  of  all  the  organs  of  the  body. 
Among  the  higher  animals,  no  cell  of  the  body  does  any 
work  except  under  the  direction  of  the  nervous  system. 

338.  Study    of    a    Vertebrate.  —  Observation    of    some 
living  vertebrate  animal  will  help  greatly  in  the  study  of  the 
organs  and  motions  of  higher  animals.     For  this  purpose  a 
goldfish  may  be  used.     It  is  easily  procured  from  a  dealer 
in  household  pets,  and  with  a  little  care,  will  live  a  long  time 
in  a  jar  of  water.     Part  of  the  water  should  be  removed  and 
fresh  water  supplied  once  a  week.     If  green  water  plants  are 
living  in  the  jar,  the  water  need  not  be  changed  so  often. 
Prepared  fish  food,  as  well  as  the  water  plants,  can  usually 
be  procured  where  the  fish  is  bought. 

339.  The    Sense    Organs    of   the    Fish.  —  Two  parts  of 
the  fish's  body  are  specially  fitted  to  receive  impressions 
caused  by  light.     These  are  the  eyes.     There  is  one  eye  on 
each  side  of  the  head.     They  are  somewhat  convex,  but  do 
not  protrude  much  beyond  the  horny  frame  in  which  they 
are  set.     Experiments  show  that  fish  are  nearsighted,  so  they 
probably  cannot  perceive  objects  at  any  great  distance. 


THE   LIFE   OF   AN   ANIMAL  293 

Experiments  in  feeding  fishes  show  that  they  become 
aware  of  the  presence  of  food  by  smelling  it  as  well  as  by 
seeing  it.  The  nostrils  of  a  fish  are  sensitive  to  substances 
dissolved  in  the  water  in  which  the  fish  lives,  as  our  nos- 
trils are  sensitive  to  gases  carried  by  the  air.  Their 
nostril  openings  end  in  little  pits  which  do  not  connect  with 
the  throat,  as  do  ours. 

The  sense  of  taste  is  located  on  the  tongue  of  the  fish, 
and  the  sense  of  touch  is  located  in  the  skin.  Both  of 
these  appear  to  be  less  developed  than  the  other  senses. 

The  fish  has  an  ear  under  the  skin  back  of  each  eye  and 
lying  wholly  within  the  skull.  It  is  like  the  internal  parts 
of  our  ears,  and  is  sensitive  to  vibration  in  the  water,  just 
as  the  ears  of  land  animals  respond  to  vibrations  of  the 
air.  (LABORATORY  MANUAL,  Exercise  XXXI.) 

340.  The  Relation  of  Sensation  to  Motion.  —  In  order 
to  live  and  reproduce  its  kind,  an  animal  must  be  able  to 
protect  itself  from  danger  and  to  secure  food.     Therefore  it 
is  provided  with  the  means  of   defense  or  the  means  of 
escape  from  enemies,  and  with  the  power  of  motion.     When 
any  change  of  surroundings  affects  the  sense  organs,  the 
nerves  send  impulses  to  the  brain  or  spinal  cord,  and  they 
in  turn  send  impulses  to  the  muscles. 

341.  Useful  Responses.  —  If  animals  respond  to  external 
conditions  in  a  way  advantageous  to  themselves,  they  will 
succeed  in  getting  food  and  in  escaping  from  danger.     Hence 
they  are  the  more  likely  to  live  long  and  to  leave  descendants. 
There  is  a  probability  that  the  young  will  inherit  from  the 
parents  the  inclination  to  respond  in  the  same  way.     As  a 
result,  instincts  may  originate  and  be  perpetuated. 

Instinct  may  be  defined  as  an  inherited  habit.  For 
example,  a  little  kitten  that  has  never  seen  a  mouse  is 
at  once  on  the  alert  at  the  sound  of  a  slight  scratching. 
It  sits  motionless  watching  the  point  from  which  the 
sound  comes.  The  kitten  is  trying  to  catch  its  prey  in  the 


294      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


same  way  that  its  parents,  its  grandparents,  and  all  its 
ancestors  did.  They  lived  to  adult  life  because  they  suc- 
ceeded in  their  methods.  The  kitten  has  inherited  the 
habits  of  the  race. 

342.   The    Structure    of    Muscles.  —  In  the  simplest  ani- 
mals, the  entire  body  is  concerned  with  the  process  of  moving. 

In  the  higher  animals, 
movements  are  brought 
about  by  organs  called 
muscles.  Muscles  are 
voluntary  or  involun- 
tary, according  to  their 
control  by  the  animal. 
The  muscles  which  may 
be  controlled  by  the  will 
are  voluntary  muscles. 
They  consist  of  masses 
of  elongated  cells  lying 
parallel  to  one  another 
and  arranged  in  small  bundles,  which  also  lie  parallel  to  one 
another.  These  bundles  may  easily  be  seen  in  boiled  meat, 
where  they  tend  to  separate  from  one  another  as  strings  or 
fibers.  Each  end  of  a  muscle  is  firmly  attached  by  a  tough 
gristly  cord,  called  a  tendon,  to  some  part  of  the  body  —  gen- 
erally to  a  bone. 

The  involuntary  muscles  are  not  fibrous  in  structure  and 
are  not  under  the  control  of  the  animal.  The  muscles  of  the 
digestive  organs  show  the  structure  of  involuntary  muscles. 
343.  The  Work  of  Muscles.  —  In  the  division  of  labor 
which  exists  among  the  cells  of  animals,  the  muscle  cells  have 
been  given  the  work  of  contraction,  or  shortening  and  thick- 
ening, but  they  act  only  under  the  direction  of  the  nervous 
system.  In  most  muscles,  all  the  cells  contract  at  the  same 
instant,  when  so  directed  by  some  part  of  the  nervous  sys- 
tem. The  muscle  .itself,  therefore,  shortens  and  grows 


FIG.  155.  —  A  BUNDLE  OF  MUSCLE 
FIBERS,     (much  magnified) 

This  picture  represents  a  "string," 
such  as  one  sees  in  boiled  lean  meat.  Each 
string  is  composed  of  hair-like  threads,  rep- 
resented by  one  of  the  small  parts  of  this 
bundle. 


THE    LIFE    OF   AN   ANIMAL  295 

thicker,  and  pulls  equally  on  the  parts  to  which  each  end  is 
attached.  Movement  occurs  in  the  part  which  offers  least 
resistence.  The  elbow  is  bent  by  a  muscle  attached  at  one 
end  to  a  bone  below  the  elbow,  and  at  the  other  to  a  bone 
above.  When  this  muscle  contracts,  the  forearm  and  hand 
move  up,  unless  opposed  by  outside  force. 

344.  Antagonistic  Muscles.  —  A  part  of  the  body  that  has 
been  moved  by  a  muscle  is  returned  to  its  original  position  by 
a  pull  exerted  by  another  muscle.     The  second  muscle  is  so 
attached  as  to  pull  in  an  opposite  direction  from  the  first. 
Such  a  pair  of  muscles  are  called  antagonistic  muscles.     For 
example,  the  knee  is  bent  by  the  contraction  of  a  muscle  on 
the  back  of  the  leg,  attached  at  one  end  to  a  bone  below  the 
joint,  and  at  the  other  end  to  a  bone  above  the  joint.     The 
knee  is  straightened  by  the  contraction  of  another  muscle  on 
the  front  of  the  leg  attached  to  the  same  bones.     One  of  the 
antagonistic  muscles  must  relax  when  the  other  contracts, 
if  movement  results;  but  there  is  nothing  in  the  relaxing  of 
a  muscle  to  exert  a  push  and  so  to  cause  movement.     Any 
motion  of  any  part  of  the  body  is  caused  by  a  pull.     Of 
the  pair,  the  muscle  which  bends  the  joint  is   called  the 
flexor,  and  that  which  straightens  it  is  the  extensor. 

345.  Organs    of    Locomotion.  —  The    organs   which    are 
specially  designed  for  the  moving  of  an  animal  from  place  to 
place  are  organs  of  locomotion.     The  fins  of  a  fish,  the  wings 
and  legs  of  a  bird,  and  the  legs  of  a  quadruped  and  of  man  are 
organs  of  locomotion.     Animals  designed  for  rapid  motion 
have,  as  a  rule,  somewhat  wedge-shaped  bodies  with  the  edge 
of  the  wedge  projected  forward.     The  fish  is  propelled  by  a 
movement  of  the  tail  fin  and  the  hinder  part  of  the  body, 
similar  to  the  movement  of  an  oar  used  in  the  stern  of  a  boat 
for  sculling. 

The  turning  movements  of  a  fish  are  brought  about  by 
the  use  of  the  paired  fins.  One  pair  of  fins  corresponds  to 
the  arms  of  man,  to  the  forelegs  of  a  dog,  and  to  the  wings  of 


296      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

a  bird.     The  other  pair  corresponds  to  the  legs  of  man  and  to 
the  hind  limbs  of  the  other  animals  mentioned.     The  single 
fins  on  the  upper  and  lower  parts  of  the  body  of  the  fish  are 
useful  for  balancing  and  for  steering. 
In  the  nervous  system  and  in  the  muscles,  animals  have 


A  B 

FIG.  156.  —  ORGANS  OF  LOCOMOTION 

Figure  A  represents  the  skeleton  of  a  fin  of  a  fish;   B  that  of  the  fore 
leg  of  a  frog;  C  that  of  the  wing  of  a  bird. 

special  organs  which  make  evident  use  of  the  properties  of 
irritability  and  spontaneous  motion.  These  properties  are 
not  less  necessary  to  the  plant,  but  they  are  not  so  easy  to 
observe  in  plants  as  in  the  higher  animals.  Responses  to 
external  influence  on  the  part  of  animals  are  more  imme- 
diate than  in  the  case  of  plants,  and  the  motion  is  more 
rapid  and  greater.  Very  few  land  plants  move  from  place 
to  place;  most  land  animals  do  so.  In  the  case  of  animals, 
there  may  be  not  only  spontaneous  motion  of  protoplasm 
within  the  cell  wall,  and  of  the  organs  of  the  body,  but  also 
locomotion,  —  that  is,  motion  of  the  whole  body  from  one 
place  to  another. 


THE   LIFE    OF   AN   ANIMAL  297 


EXERCISES 

1.  Name  three  differences  between  simple  and  complex  organisms. 

2.  What  is  the  function  of  the  nervous  system? 

3.  Name  three  sense  organs. 

4.  Of  what  use  are  the  sense  organs  in  our  finger  tips? 

5.  Give  an  example  of  an  animal  that  has  a  keen  sense  of  smell;  of 
hearing;  of  sight. 

6.  (a)  Give  an  example  of  instinct  shown  by  a  bird.     (6)  An  ex- 
ample which  shows  that  some  animal  has  been  taught  by  man. 

7.  What  are  vertebrates?     Name  four  different  examples. 

8.  How  do  muscles  act  to  produce  motion  of  a  part  of  the  body? 

9.  Give  some  illustration  of  antagonistic  muscles  not  mentioned 
in  the  text. 

10.   On  which  side  of  a  fish's  body  is  the  muscle  which  moves  the 
tail  to  the  left?    What  is  that  kind  of  muscle  called? 


CHAPTER  XXVI 
REPRODUCTION  AND   DEVELOPMENT   OF   ANIMALS 

346.  Reproduction.  —  In  animals,  as  in  plants,  the  func- 
tion of  reproduction  is  a  function  belonging  to  maturity. 
The  power  of  reproduction  is  not  essential  to  the  life  of  an 
individual  animal  but  is  essential  to  the  continuance  of  a 
race  of  animals. 

347.  Reproductive  Organs.  —  In  the  higher  animals,  as 
in  the  higher  plants,  there  are  certain  organs  the  function  of 
which  is  to  provide  for  the  making  of  other  animals.     These 
organs  are  called  reproductive  organs.     As  in  the  higher 
plants,  these  organs  are  of  two  kinds:    one  kind  producing 
inactive  cells,  called  egg  cells  or  eggs,  such  as  are  formed  in 
the  ovule  of  the  flower;  the  other  kind  producing  very  small 
active  cells,  called  sperm  cells  or  sperms,  such  as  are  found  in 
the  pollen  grains  of  the  stamen  of  a  flower.     Fertilization, 
that  is,  the  bringing  together  of  the  cells  of  the  two  kinds,  is 
generally  necessary  for  the  development  of  a  new  animal 
organism.     The  number  of  eggs  produced  varies  with  different 
animals,  just  as  the  number  of  seeds  varies  with  different 
plants.     Insects  and  common  fishes  deposit  many  eggs  at  a 
time;  birds,  a  few.     Some  animals  reproduce  many  times  in 
a  season,  some  once  a  year,  and  some  higher  animals  less 
frequently. 

348.  Sex.  —  In  animals,  as  in  some  plants,  both  kinds  of 
reproductive  organs  may  exist  in  one  individual  organism, 
but  generally  there  is  only  one  kind  of  organ  in  an  individual. 
Animals  having  only  egg-producing  organs,  ovaries,  are  called 
females ;  those  having  only  sperm-producing  organs,  sperma- 
ries,  are  called  males.    With  the  egg  cell,  the  female  furnishes 

298 


REPRODUCTION  AND  DEVELOPMENT  OF  ANIMALS  299 


nourishment  for  each  developing  animal.  This  nourishment, 
when  attached  to  the  egg  cell  and  enclosed  in  an  egg  covering, 
is  known  as  yolk. 

349.  The  Care  of  the  Young.  —  As  a  rule,  the  animals 
which  have  small  egg?  produce  many.  Worms,  lobsters, 
insects,  fishes,  and  frogs  deposit 
small  eggs  in  immense  numbers; 
birds  and  reptiles  produce  larger 
eggs  in  fewer  numbers.  The  care 
given  to  the  eggs  is  greater  when 
a  small  number  is  produced.  Some 
reptiles  and  all  birds  have  eggs 
with  a  tough  or  hard  covering. 
Fishes,  worms,  and  other  water 
animals  have  soft,  jelly-like  eggs. 

The  development  of  the  embryo 
begins  in  the  same  way  as  in  the 
plant:  the  egg  cell  divides  and 
subdivision  .continues  until  the 
young  animal  is  completely 
formed.  In  the  case  of  the 
highest  class  of  vertebrate 
animals,  the  egg  cell  remains  and 
is  nourished  in  the  body  of  the  female  for  a  longer  or 
shorter  time.  After  the  birth,  the  female  continues  to 
furnish  protection  and  nourishment'  for  weeks  and  even 
months.  This  nourishment,  the  milk,  contains  proteid,  fat, 
sugar,  and  mineral  matter  dissolved  in  water.  This  is  all 
the  food  the  young  animal  needs  until  it  is  able  to  digest 
solid  foods. 

Birds  care  for  their  eggs  during  the  period  of  development 
of  the  embryo,  and  a  few  species  of  fishes  make  nests  and 
guard  them,  but  usually  the  eggs  of  fishes  are  left  to  develop 
alone.  The  same  is  true  of  reptiles  and  insects.  As  soon  as 
the  food  provided  in  the  yolk  is  used  up,  the  eggs  hatch  and 


FIG.  157.  —  REPRODUCTIVE 
CELLS  (magnified) 

a  is  an  egg  cell  of  a  frog, 
b,  a  sperm  cell.  The  union  of 
such  cells  results  in  the  forma- 
tion of  an  egg,  such  as  is  shown 
in  B,  Fig.  158. 


300     FIRST    YEAR    COURSE    IN    GENERAL    SCIENCE 

the  little  animals  begin  to  seek  their  own  food.  Only  a  very 
small  proportion  of  the  eggs  deposited  ever  hatch,  because 
large  numbers  of  the  eggs  are  food  for  other  animals.  Of 
those  that  hatch,  only  a  small  percentage  lives  to  reproduce, 
because  the  young  become  the  prey  of  other  animals  and 
man.  The  shad  lives  upon  small  organisms,  vegetable  and 
animal,  and  the  bluefish  eats  young  fish,  even  its  own  kind. 
In  order  to  preserve  wild  game,  it  has  been  found  neces- 
sary to  make  laws  prohibiting  the  hunting  of  animals  at  cer- 


FIG.  158.  —  EGGS 

Figure  A  is  a  cluster  of  eggs  of  a  salamander;  B,  eggs  of  a  frog.  These 
eggs  are  surrounded  by  a  transparent  jelly-like  covering.  They  float  in 
the  water  of  ponds  and  swamps  until  hatched.  Figure  C  is  the  egg  of  a 
bird;  D,  eggs  of  a  katydid. 

tain  times  in  the  breeding  season.  At  that  season,  usually 
spring  and  early  summer  in  northern  latitudes,  fish  come 
from  the  ocean  into  the  rivers  and  birds  go  to  cool  climates, 
seeking  places  to  deposit  their  eggs.  The  United  States 
Bureau  of  Fisheries  studies  the  habits  of  fishes  and  the 
relative  food  values  of  different  fishes  and  recommends  the 
making  of  laws  for  the  protection  and  artificial  hatching  of 
food  fishes.  The  Department  of  Agriculture  provides  for  the 
study  and  protection  of  useful  birds.  Larger  game  may 
safely  breed  in  public  forest  reservations. 

350.  How  Fishes  Take  Food.  —  A  fish  has  no  structures 
for  grasping  its  food,  except  teeth.  The  teeth  are  usually 
small,  sharp,  and  numerous,  well  adapted  for  holding 


FIG.  159.  —  Louis  AGASSIZ  :    ZOOLOGIST.     1807-1873 

And  Nature,  the  old  nurse,  took 

The  child  upon  her  knee, 
Saying,  "Here  is  a  story-book 

Thy  Father  has  written  for  thee." 

"Come  wander  with  me,"  she  said, 
"  Into  regions  yet  untrod,       • 
And  read  what  is  still  unread 
In  the  manuscripts  of  God." 

And  he  wandered  away  and  away 

With  Nature  the  dear  old  nurse. 
Who  sang  to  him  night  and  day 

The  rhymes  of  the  universe. 

And  wherever  the  way  seemed  long 

Or  his  heart  began  to  fail, 
She  would  sing  a  more  wonderful  song, 
Or  tell  a  more  wonderful  tale. 

HENRY  W.  LONGFELLOW 

in  The  Fiftieth  Birthday  of  Agassiz 


302     FIRST    YEAR   COURSE    IN    GENERAL    SCIENCE 


living  prey.  Birds  and  most  fishes  do  not  chew  food  in  the 
mouth,  and  so  the  tongue  —  which  in  many  animals  is  used 
to  move  and  hold  the  food  in  chewing  —  is  lacking  or  is 
developed  only  to  assist  in  swallowing.. 

351.  Breathing  Movements.  —  The  mouth  of  the  fish 
makes  certain  movements  which  look  like  biting,  though  there 
is  no  food  present.  If  we  put  some  grains  of  colored  matter 
into  the  water,  we  can  see  them  being  drawn  into  the  mouth 
and  passing  out  through  slit-like  openings  on  the  side  of  the 
head,  back  of  the  mouth.  These  movements  are  breath- 
ing movements  which  allow 
the  water,  containing  dis- 
solved oxygen  from  the  air, 
to  pass  over  the  breathing 
organs,  called  gills. 

352.  Breathing  Organs.  — 
The  gills  of  water  animals  are 
covered  by  thin  plates,  one 
on  each  side  of  the  head, 
called  gill  covers,  which  lift 
at  one  side  to  let  the  water 
pass  out.  The  gills  look  like 
.fine  red  fringes  attached  to 
curved  bony  frames.  In  the 
" threads"  of  the  fine  fringes, 
blood  is  flowing  all  the  time. 
It  receives  oxygen  through  the 
membranes  by  osmosis,  and  discharges  into  the  water  the 
waste  product,  carbon  dioxide.  The  work  of  the  gills 
of  water  animals  is  similar  to  the  work  done  by  the  lungs 
of  land  animals. 

The  breathing  organs  of  vertebrate  animals  that  live  in 
air  are  lungs.  They  are  elastic  bags  of  spongy  tissue  con- 
tained in  a  cavity  in  the  forward  or  upper  part  of  the  body. 
An  air  passage  leads  from  the  nostrils  into  the  lungs,  where 


FIG.  160.  —  Am  SAC  IN  THE  LUNGS 

a,  an  artery;  v,  a  vein;  p,  air  tube. 

The  direction  of  gases  passing 
between  the  air  sac  and  the  blood 
vessels  is  shown  by  arrows.  Which 
represent  the  oxygen? 


REPRODUCTION    AND   DEVELOPMENT    OF  ANIMALS  303 

it  divides  again  and  again  into  minute  tubes.  At  the  end  of 
every  tube  is  a  little  air  sac.  The  walls  of  the  air  sacs  are 
very  thin  and  on  their  surface  lie  blood  vessels  of  minute 
size.  Oxygen  from  the  air  passes  by  osmosis  into  the  blood 
vessels  from  the  air  sacs.  Carbon  dioxide  and  water  vapor 
pass  out  of  the  blood  vessels  into  the  air  sacs.  In  this 
manner,  these  waste  products  are  excreted  from  the  body 
by  the  same  organs  which  receive  the  oxygen. 

353.  The  Need  of  Digestion.  —  As  in  the  case  of  plants, 
so  in  animals,  it  is  necessary  that  the  food  be  changed  into 
soluble  substances  and  then  dissolved,  in  order  that  it  may  be 
distributed  to  all  parts  of  the  body.     Digestion  is  carried  on 
in  a  tube  called  the  alimentary  canal,  which  extends  through 
the  body.     It  has  two  openings:  one,  the  mouth,  for  the  re- 
ception of  food;  the  other,  the  anus,  for  the  expulsion  of  any 
indigestible  residue.     The  walls  of  the  alimentary  canal  con- 
tain  circular    involuntary   muscles,  which    by  contracting 
slowly  push  the  food  along.     There  is  no  opening  from  this 
tube  into  the  other  parts  of  the  body.     The  substances  that 
enter  the  tissues  of  the  body  from  this  tube,  must  pass 
as  liquids  through  its  walls,  which  are  non-porous.     Hence, 
food  must  be  digested,  that  is,  made  soluble  and  capable  of 
osmosis. 

354.  The  Parts  of  the  Alimentary  Canal.  —  Behind  the 
mouth,  the  gullet  of  a  fish  and  of  other  vertebrates  broadens 
into  a  baglike  stomach,  an  important  part  of  the  alimentary 
canal,  where  the  food  is  thoroughly  mixed  with  digestive 
fluids  formed  in  the  walls  of  the  stomach.     These  liquids 
produce  chemical  changes  in  the  food  whereby  some  of  it 
becomes  soluble.      It  is  then  dissolved  and  in  part  soaks 
through  the  walls  of  the  stomach  into  blood  vessels  and 
is  carried   by  the   blood  currents  to  the  different  organs 
that  require  it.     Food  not  digested  in  the  stomach  passes 
into   the   small    intestine,  the  next   portion   of   the   tube. 
Here   the   food   is   mixed   with  other    liquids   formed    by 


304     FIRST   YEAR    COURSE    IN    GENERAL    SCIENCE 

other  digestive  organs,  so  that  further  digestion  may  be 
accomplished.  From  the  small  intestine  the  contents  are 
pushed  into  the  large  intestine,  where  digestion  is  com- 
pleted. In  this  part  of  the  canal,,  the  water  which  is 
no  longer  needed  for  solution  is  absorbed  through  the 
walls. 

355.  Indigestible  Residue.  —  Whatever  parts  of  the  food 
have  not  been  digested  before  reaching  the  end  of  the  alimen- 
tary canal  are  expelled  through  the  anus,  or  posterior  open- 
ing. These  parts  are  not  waste  products  but  an  indigestible 


'a/b  ' 
FIG.  161.  —  THE  ALIMENTARY  CANAL  OR  FOOD  TUBE  OF  A  FISH 

Observe  the  continuous  passage  from  the  mouth  (a),  through  the 
stomach  (c)  and  the  intestine  (d),  to  the  anus  (e).  b  shows  the  gills  and 
gill  rakers. 

residue.  Though  they  have  passed  through  the  body,  they 
have  never  been  a  part  of  the  body.  Grains  of  sand  might 
enter  the  mouth  with  other  food,  but  being  insoluble,  would 
pass  unchanged  through  the  stomach  and  intestines  and  be 
expelled. 

Animals  living  mainly  upon  plant  food  take,  with  the 
nutritious  part,  much  that  is  indigestible.  This  is  not  an 
injury  but  a  benefit,  because  it  prevents  the  close  packing 
together  of  the  substances  which  must  be  acted  upon  by  the 
solvents.  Pure  starch  is  not  so  good  a  food  as  a  potato, 
whose  bulk  is  mainly  pith  cells  containing  starch.  After 
mastication,  the  starch  is  mixed  with  the  covering  of  the 


REPRODUCTION    AND    DEVELOPMENT   OF  ANIMALS  305 

cells,  called  cellulose,  making  a  spongy  rather  than  a  pasty 
mass.  The  digestive  fluids  can  readily  attack  the  starch, 
while  the  cellulose  becomes  a  part  of  the  indigestible 
residue. 

356.  Blood.  —  In  all  the  higher  animals  there  is  a  liquid, 
the  blood,  that  is  driven  through  the  body  by  a  force  pump, 
the  heart.     The  blood  travels  through  a  system  of  tubes 
called  blood  vessels.     This  liquid  is  useful  in  distributing 
food  and  oxygen  among  the  cells,  and  in  collecting  and  carry- 
ing away  from  them  the  waste  products  from  oxidation. 
The  blood  carries  the  carbon  dioxide  and  water  vapor  to  the 
breathing  organs,  and  nitrogen  compounds  and  water  to  the 
kidneys.      The    kidneys    of    vertebrates    are    two    organs 
located  inside  the  body  near  the    anus,   and   opening    by 
tubes  to  the  outside  of  the  body. 

357.  Body  Temperatures.  —  In  the  body  of  such  animals 
as  worms,  fishes,  and  frogs,  oxidation  is  slower  than  it  is  in 
many  other  animals,  and  so  the  heat  generated  in  oxidation 
does  not  raise  the  temperature  of  the  blood  perceptibly  above 
that  of  the  water  in  which  these  animals  live.     For  this  rea- 
son certain  animals  have  commonly,  though  inaccurately, 
been  given  the  name  "  cold-blooded."     The  actual  tempera- 
ture of  the  body  of  a  cold-blooded  animal  changes  with  the 
temperature  of  its  surroundings. 

In  warm-blooded  animals,  the  body^  maintains  a  certain 
relatively  high  temperature  all  the  time,  regardless  of  the 
temperature  of  the  surroundings.  The  temperature  of  the 
blood  in  the  human  body  in  health  is  slightly  above  98°  F. 
In  some  birds  it  is  higher  than  that. 

358.  The  Two  Uses  of  Food.  —  The  oxygen  and  digested 
foods  that  are  distributed  by  the  blood  are  taken  up  by  the 
different  cells  and  are  transformed  into  living  protoplasm, 
resulting  in  growth.     Then  as  each  cell  does  its  work,  part  of 
the  substance  is  oxidized  to  release  the  energy  for  this  work 
and  the  temperature  is  kept  at  the  degree  required. 


306     FIRST    YEAR    COURSE    IN    GENERAL    SCIENCE 

359.  The  Processes  of  Animal  Nutrition.  —  Thus  it  is 
seen  that  in  animals  and  in  plants  nutrition  consists  of  the 
same  essential  stages: 

The  taking  in  of  food  and  oxygen.  • 

The  digestion  of  food. 

The  transforming  of  food  into  live  tissues. 

The  oxidation  of  that  tissue  to  yield  energy. 

The  excretion  of  the  waste  products  resulting  from 
oxidation. 

The  elimination  of  the  indigestible  residue  left  from 
digestion. 

EXERCISES 

1.  What  is  the  importance  of  reproduction? 

2.  Why  is  it  not  necessary  that  a  bird  should  lay  as  many  eggs  as 
a  fish,  in  order  to  continue  the  race? 

3.  What  similar  provision  is  made  by  plants  and  animals  for  the 
early  development  of  their  offspring? 

4.  What  relation  has  the  amount  of  nourishment  in  an  egg  to  the 
size  of  the  animal  that  hatches  from  it?     Illustrate. 

6.  Does  the  care  of  a  few  young,  or  the  production  of  a  large  num- 
ber of  offspring  that  receive  no  care,  give  better  results  to  the  race? 
Give  instances  that  illustrate  your  answer. 

6.  (a)  Suggest  a  reason  why  grass  cannot  serve  as  food  for  a  dog. 
(b)  Why  cannot  a  horse  subsist  on  meat? 

7.  Why  does  the  loss  of  much  blood  cause  death? 

8.  (a)  Account  for  the  different  amounts  of  food  required  by  cold- 
blooded and  by  warm-blooded  animals.     (6)  What  is  the  value  of  the 
hair  or  the  feathers  covering  the  bodies  of  most  warm-blooded  animals? 

9.  To  what  organisms  are  the  excreted  waste  products  of  animals 
useful,  and  for  what  purpose? 

10.  What  waste  product  of  plants  do  animals  require? 

11.  Explain  how  some  hibernating  animals  are  able  to  live  without 
food  for  a  long  time. 

12.  Through  what  organs  do  animals  excrete  carbon  dioxide? 


INDEX 

lAn  asterisk  following  a  page  number  indicates  an  illustration.) 


Acids,  160 

Agassiz,  Louis,  301  * 
Agriculture,  science  of,  164 
Air,  composition,  149 

density,  96  * 

how  warmed,  77 

humidity,  107 

sac,  302  * 

saturated,  107 

solution  in  water,  94  * 
Aldebaran,  15,  19 
Alimentary  canal,  303 

of  fish,  304  * 
Alloy,  153 
Altitude,  117 
Aluminum,  154 
Amalgams,  155 
Analysis,  chemical,  158 
Animals,  care  of  the  young,  299 

carnivorous,  260 

herbivorous,  260 

need  of  food,  259 

omnivorous,  260 

one-celled,  289  * 

processes  of  nutrition,  306 

relation  to  plants,  260  * 

reproductive  organs,  298 
Antagonistic  muscles,  295 
Antares,  16 
Anthers,  276,  277  * 
Anthracite,  186 
Antidotes,  165 
Apparatus,  62 
Arc  lights,  136 
Arctic  circle,  25 
Asbestos,  172 
Asphyxiation,  141 
Astronomy,  ancient,  13,  19 
Atmosphere,  variations  in  composi- 
tion, 107 
Atmospheric  pressure,  95 

differences,  96  *,  98 


Atmospheric  pressure,  direction,  100 

on  the  body,  98 
Atom,  156 
Axle,  59,  60 
Axon,  291 

Balance,  equal  arm,  63,  64  * 

spring,  63  * 
Barometer,  97,  98 
Bases,  161 
Bean  plant,  265 

flower,  276 

ovary,  278,  279  * 

structure  of  seed,  278,  279 
Bell,  electric,  135 
Belt  of  Calms,  113 
Big  Dipper,  16,  17  *,  18  *,  19 
Blast  furnace,  169  * 
Block  mountains,  203  * 
Blood  vessels,  305 
Body,  definition,  47 

temperatures,  305 
Boiling  point,  68 
Boulders,  248 
Brittleness,  54 
Brownstone,  180 
Bunsen  burner,  142  *,  143 

Calcite,  172 

Calendar,  28,  29 

Caloric,  77 

Camera,  125,  126  * 

Candle  power,  120 

Canis  Major,  16 

Capacity,  measurement  of,  52,  53  * 

Capillarity,  90,  91  * 

Carbon,  150 

Carbon  dioxide,  an  important  oxide, 
159 

excretion  of,  160,  258 
fire  extinguisher,  144  *,  145 
307 


308      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


Carbon  dioxide,  in  the  lungs,  303 

in  water,  94 

relation  to  life,  160  * 
Carbonated  water,  94 
Carbonates,  163 
Care  of  the  young,  299 
Cassiopeia,  17,  18  *,  19 
Cast  iron,  153 
Celestial  meridian,  27  * 
Cells,  division,  263,  264  * 

growth,  264 

in  surface  of  a  leaf,  268  * 
Centigrade  thermometer,  73  * 
Changes  of  level,  193 
Charcoal  making,  71,  72  *,  150 
'  Chemical,  change,  48,  138 

engines,  145 

symbols,  155 
Chlorine,  150 
Chlorophyll,  coloring  in  plants,  259 

grains,  268  *,  270 

in  starch  making,  270 
Clay,  171 
Climate,  78,  116 

changes,  118 
Coal,  150,  185 

anthracite,  186 

bituminous,  186 

fields,  186  * 

Colorado  Canyon,  237  * 
Combination,  139 
Combustion,  140 

spontaneous,  140 
Compass,  magnetic,  133  * 
Compounds,  47 

classes,  159 
Condensation,  68 
Conduction  of  heat,  74  * 
Conductivity,  152 
Conductors,  of  heat,  75 

of  electricity,  129 
Conglomerates,  180 
Conservation    of    Matter,    Law    of, 

142 
Constellations,  15,  18* 

reasons  for  studying,  18 
Continental  block,  191  * 
Continents,  190 

changes  of  level,  193,  194  * 

changes  in  size,  192,  240 

location  in  relation  to  history, 
195 


Continents,  relation  to  water,  190 
story  told  by  rocks,  191 

Contour,  intervals,  216,  218 
lines,  216,  218,  220 
maps,  216,  217  *,  220,  224  * 

Convection,  75 

Copper.  153 

Coral  reefs,  192  * 

Corn  seedling,  280 

Corona,  16 

Crystals,  168  * 

Currents,  in  convection.  75 
electric,  133 
ocean,  197 

Cyclonic  movements,  112 

Dana,  James  D wight,  171  * 

Day,  23,  25 

Decomposition,  139 

Definite  Proportions,  Law  of,  142 

Degradation,  202,  205     ' 

Density,  definition,  63 

of  air,  96  * 

of  a  liquid,  66 

of  a  solid,  65  * 

methods  of  determining,  65,  66 
Denudation,  205 
Dew  point,  107 
Diffusion,  94  *,  95 
Digestion,  in  animals,  303 

in  plants,  272 
Dikes,  183  * 
Dissolving,  82 
Distillate,  68 
Distillation,  68,  69  * 

fractional,  69 

uses,  69 
Divers,  86,  87  * 
Dog  days,  16 
Dog  star,  16 
Drift,  glacial,  248 
Ductility,  152 
Dynamo,  136* 

Earth,  age,  187 
a  planet,  33 
axis,  24 

crust,  167  *,  177 
early  beliefs,  13 
revolution,  22,  34 
rotation,  21 
shape,  14 


INDEX 


309 


Earthquakes,  causes,  225 

effects,  225  *,  226,  227  * 

famous,  226 
Eclipses,  of  the  moon,  42,  43  *,  44  * 

of  the  sun,  42,  43  * 
Eggs,  298,  300  * 
Elasticity,  54 
Electric,  battery,  132  * 

cell,  132  * 

circuit,  132 

current,  133 

dry  cell,  133 

lights,  136 

Electrical  machine,  130  * 
Electricity,  and  magnetism,  135 

current,  131 

frictional,  128 

positive  and  negative  charges, 
128 

statical,  129 

voltaic,  131 
Electrodes,  132 
Electrolysis,  148  * 
Elements,  definition,  47 

number,  47 

principal,  47 
Elevators,  81 
Embryo,  278 
Energy,  58,  254 

and  heat,  79 

transformation,  136 
Engines,  chemical,  145 

cylinder  of,  79 

gas,  61 

steam  chest  of,  79  * 
Equator,  25 
Erosion,  202,  237 
Eruptions,  229,  230 
Excretion,  258 

animal,  257,  306 

of  carbon  dioxide,  160,  303 

of  water,  269 

plant,  257,  269,  273,  274 
Experiment,  definition,  61 
Explosions,  140 
Explosives,  140 
Extension,  49 

measurement,  50  * 
Eye,  125,  126  * 
Eye  glasses,  126 

Fahrenheit  thermometer,  72 


Fault,  225 

Feldspar,  171 

Fertilization  of  flowers,  277,  278 

Fertilizers,  164,  165  * 

Fire  extinguisher,  144  *,  145 

Fish,  alimentary  canal,  304  * 

a  type  of  vertebrate,  292 

breathing  organs,  302 

ears,  293 

manner  of  taking  food,  300 

nostrils,  293 

organs  of  taste  and  touch,  293 

sense  organs,  292 
Fissures,  183 
Flexibility,  54 

Flowerless  plants,  280,  281  * 
Flowers,  behavior,  283 

fertilization,  277 

pollination,  277,  278  * 

structure,  276 
Floods,  238  * 
Flux,  169 

Folded  mountains,  203 
Folded  rock,  182,  185  *,  204  * 
Food,  255 

amount  required,  257 

need  of,  257 

residue,  258 

stored  in  seed,  256  *,  272 

two  uses,  305 
Force,  56 

pump,  104  *,  105 
Forces  at  right  angles,  57,  58  * 
Forestry,  210,  211 
Forests,  209 

and  rainfall,  212 

enemies,  212,  213  * 

importance,  214 
Formulas,  chemical,  158 
Fossils,  188  *,  193  * 
Freezing  point,  68 
Friction,  57 
Fruit,  278 

Functions,  definition,  255 
Furnace,  143  * 
Fusibility,  152 

Garden  of  Gods,  Manitou,  Colorado, 

187* 

Gases,  definition,  67 
diffusion,  94  *,  95 
molecular  motion,  93 


310      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


Gases,  properties,  93 

relation   between  pressure    and 
volume,  101  * 

solubility,  93 
Gems,  170 

Generator  of  electricity,  136  * 
Germination,  process,  279 

result,  279 
Glacial,  drift,  248 

lakes,  248,  249  * 
Glaciated  rock,  247  * 
Glacier,  beginning,  244 

in  Switzerland,  245  *,  246  * 

retreat,  246 

work,  245 
Gneiss,  182 
Gold,  153 
Granite,  formation,  178 

quarry,  178  * 

use,  179 

Gray,  Asa,  271  * 
Great  Bear,  17,  18  * 
Growth  movements,  of  cells,  263 

of  plants,  282 
Gulf  Stream,  197 
Gypsum,  174 

Hachure  maps,  216,  217  * 

Hardness,  53 

Heat,  absorbed  by  water,  78 

and  energy,  79 

conduction,  74 

convection,  75 

effects,  67,  71 

intensity,  77 

quantity,  77 

radiation,  75 

sources,  71 

vertical  and  oblique  rays,  116, 

117* 

Henry,  Joseph,  131  * 
Hornblende,  172 
Hot  water  heating,  76  * 
Hydraulic  presses,  81,  82  * 
Hydrogen,  148* 

Igneous  rock,  178 
Ignition  point,  141 
Incompressibility,  81 
Incandescence,  120 
Incandescent  lights,  136 
Indigestible  residue,  304 


Inertia,  52 
Inorganic  matter,  55 
Instinct,  293 
Insulators,  129 
Iron,  152 

reduction,  169 
Irrigation,  242 
Irritability,  definition,  54 

in  animals,  254 

in  plants,  254,  285 

Japan  Current,  197 
Jupiter,  33,  34,  35  *,  36,  37 

Kindling  point,  141 

Lakes,  causes,  248,  249,  250 

glacial,  248,  249  * 

sources  of  rivers,  250 

uses,  250 
Lava,  179 

sheets  and  dikes,  231 
Latitude,  28 

Laws,   of  Conservation  of   Matter, 
142 

of  Definite  Proportions,  142 

of  liquid  pressure,  88,  90. 
Lead,  155 
Leaves,  cells,  268  * 

chlorophyll  grains,  268  *,  270 

compound,  267  *,  268 

functions,  268 

simple,  267  *,  268 

starch  making,  269 
Lenses,  123,  125* 
Leo,  16,  21,  33 
Lever,  59,  60  * 
Lift  pump,  103,  104  *,  105 
Light,  a  form  of  energy,  121 
Light,  absorbed,  121 

a  form  of  energy,  121 

in  starch  making,  270 

influence  on  plants,  282,  283  *, 
284 

intensity,  120 

reflected,  121,  122  * 

refracted,  123  *,  124  * 

sources,  120 

transmitted,  121 
Lightning,  115,  129 
Limestone,  180 

quarry,  181  * 


INDEX 


311 


Liquid  pressure,  86 

direction,  88 

in  a  hot-water  boiler,  89  * 

laws,  88  *,  90 
Liquids,  definition,  67 

buoyancy,  90 

pressure,  86-90 

properties,  81 
Litmus  paper,  160 
Little  Bear,  17,  18  * 
Little  Dipper,  17  *,  18  * 
Locomotion,  organs,  295* 
Longitude,  28,  29 
Lunar,  eclipse,  42,  43  * 

shadow,  44  * 
Luster,  152 

Machines,  59,  60  *,  61,  62  * 
Magnesium,  155 
Magnetic  compass,  133  *,  134 
Magnetic  needle,  134  * 
Magnetism,  134 

and  electricity,  135 
Magnifying  glass,  125  * 
Malleability,  152 
Mantle  rock,  167,  234 
Map  making,  216 
Marine  life,  199 
Marble,  formation,  174 

uses,  174  . 

Mars,  33,  34,  35  *,  36,  37 
Matter,  definition*  46 

divisions,  47 

inorganic,  55 

living,  254 

organic,  55,  254 

physical  states,  67 
Measures,  systems  of,  49,  50  * 
Melting  point,  67 
Mercuric  oxide,  139 
Mercury  (metal),  154 

(planet),  33,  35*.  36 
Meridian,  27  *,  29,  30 
Metals,  native,  153 

properties,  152 

specific  gravity,  155 

uses,  155 

Metamorphic  rocks,  182 
Metric  system,  49 
Mica,  172 
Midnight  sun,  25 
Mineral  springs,  84 


Minerals,  167 

importance  of  studying,  175 

value,  184 
Mining,  206  * 
Mirror,  122  * 
Mixtures,  48 
Mobility,  81 
Molecules,  composition,  156 

definition,  46 

motion,  93 
Moon,  38,  41 

apparent  changes,  38 

eclipses,  42 

light,  39 

rotation  and  revolution,  39 

surface,  40 

time  of  rising,  40 
Moraine,  terminal,  246 
Motor  nerves,  291 
Mountains,  barriers,  208,  209  * 

block,  203 

folded,  203 

influence,  207 

making,  202 

of  erosion,  202 

railroads,  207  *,  208 
Muscles,  antagonistic,  295 

extensor,  295 

flexor,  295 

structure,  294  * 

work,  294 

Neptune,  33,  35  *,  36 
Nerve  centers,  291,  292 
Nerves,  291 

motor,  291 

sensory,  291 
Nervous  system,  290 

divisions,  290 

importance,  292 

useful  responses,  293 
Newcomb,  Simon,  34  * 
Nickel,  155 
Night,  23 
Nitrogen,  149 
North  point,  20 
North  pole,  20 
North  Star,  16,  17  *,  18  *,  19,  20 

importance  of  knowing,  20 

pointers,  16,  17  *,  18  * 
Northern  sky,  18  * 
Nucleus,  263 


312      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


Nutrition,  54 

of  animals,  255,   257,  306 
of  plants,  255,  257,  274 

Oceans,  composition,  195 

currents,  197 

depth,  195 

first,  195 

life,  199 

relation  .to  land,  190,  191  * 

temperatures,  196* 

tides,  198  * 

Opaque  substance,  122 
Ores,  168 

reduction,  168 
Organic  matter,  55,  254 
Organisms,  54 

complex,  289 

simple,  289  * 

Organs  of  locomotion,  295  * 
Orion,  15,  21 
Osmosis,  95,  302 
Ovary,  277  * 
Ovules,  277 
Oxidation,  139 

relation  to  life,  141 

waste  products,  257 
Oxides,  definition,  139 

mercuric,  139 

sulphur,  152 

two  most  important,  159 
Oxygen,  147 

burning  wire  in,  147  * 

oxyhydrogen  lamp,  147  * 

Pea  seedling,  280  * 
Pen  filler,  103  * 

Period  of  revolution,  of  the  earth, 
34 

of  the  moon,  38 

of  the  planets,  34 
Period  of  rotation,  of  the  earth,  23 

of  the  moon,  38 
Petals,  276,  277  * 
Petrifactions,  174 
Petrified  forest,  175  * 
Phosphorus,  151 
Photography,  162 
Physical  changes,  48,  138 
Pistil,  276 

Pith  ball,  electrified,  128,  129  * 
Planets,  33 


Planets,  brightness,  36 

distance,  35  *,  36 

motion,  33 

revolution,  34 

size,  36 
Plants,  digestion,  272 

excretion,  273 

flowerless,  280 

growth  movements,  281 

importance   of   chemical   work, 
271 

influence  of  contact,  285 

influence,  of  gravity,  284 

influence  of  light,  282,  283 

influence,  of  water,  285 

internal  cause  of  movement,  286 

motor  organs,  283 

need  of  food,  257,  259 

need  of  water,  259 

nutrition,  255,  257,  274 

presence  of  water  in,  269 

properties,  254 

proteid  making,  270 

relation  to  animals,  260 

respiration,  273 

starch  making,  269 

storage  of  food,  272 
Plaster  of  Paris,  174 
Platinum,  155 
Pleiades,  15 
Poisons,  165 
Pole  Star,  16,  20 
Pollen,  277 
Pollination,  277  * 
Potato  grown  in  a  cellar,  283  * 
Pressure  in  liquids,  87  *,  88  *,  89  * 
Pressure  of  the  air,  95 

differences,  96  *,  98 

direction,  100 

on  our  bodies,  98 
Prime  meridian,  29 
Prisms,  123,  124* 
Properties,  of  all  matter,  48 

of  living  matter,  54 

physiological,  254 

special,  53 

Property,  definition,  48 
Proteid  making,  270 
Protoplasm,  258 

behavior,  258 

composition,  258 

sensitiveness  to  light,  282 


INDEX 


313 


Pudding  stones,  180 
Pulley,  59,  60  * 
Pumps,  103 

air,  99  *,  100  * 

force,  104  *,  105 

lift,  103,  104  * 

suction,  103 

Quarry,  178  *,  180  *,  181  * 
Quartz,  168  *,  170 

Radiation  of  heat,  75 
Reduction  of  ores,  168,  169  * 
Reducing  agents,  168 
Reflection  of  light,  121,  122  * 
Refracting  bodies,  123 
Refraction  of  light,  121,  123  *,  124  * 
Regulus,  16,  19,  33 
Relief  maps,  216,  217  * 
Reproduction,  54,  254 

object,  276 

of  animals,  298 

of  cells,  264 

of  plants,  276 
Reproductive  organs,  of  animals,  298 

of  plants,  276 
Reservoirs,  221,  250,  251  * 
Respiration,  256 

of  animals,  302 

of  plants,  273 
Resultant,  56 
Retina,  125 
Rivers,  absence,  241 

deposit,  238 

erosion,  237 

formation,  235 

load,  236 

usefulness,  240 
Rocks,  177 

folded,  182,  185  *,  204  * 

igneous,  178  * 

making,  177,  186 

metamorphic,  182 

sedimentary,  179,  180  *,  181  * 

value,  184 

water- worn,  177  * 

weathered,  234  * 
Roots,  265 

extent,  265 

functions,  265 

primary,  265,  266  * 

secondary,  265,  266  * 


Roots,  uses,  266 

Salt  lakes,  84 
Salts,  161 

uses,  162 
Sandstone,  180 

quarry,  180  * 

Saturn,  33,  34,  35  *,  36,  37,  38  * 
Scales,  platform,  64  * 
Schist,  182 
Scorpio,  15  *,  16,  21 
Screw,  59,  60  * 
Seasons,  24 

Sedimentary  rock,  179,  180  * 
Seed  pods,  279  * 
Seed,  278 

bean,  278 

germination,  279 

Sensation,  relation  to  motion,  293 
Sense  organs,  291 

of  a  fish,  292 
Sensitive  plant,  286  * 
Sensory  nerve,  291 
Sepals,  276,  277  * 
Sex,  298 
Shales,  181 
Sickle,  16 

Silliman,  Benjamin,  159  * 
Silver,  154 

Silver  plating  bath,  163  * 
Siphon,  102* 
Sirius,  16,  19 
Slag,  169 
Snow  line,  244 
Soda  water,  94 
Soil,  234 
Solar  system,  22 
Solids,  definition,  67 
Solution',  82 
Solvents,  83 
Specific  gravity,  66 

of  metals,  155 
Spontaneous,  combustion,  140 

motion,  54,  254 
Spores,  281 
Springs,  86 

fissure,  85,  86  * 

mineral,  84 

surface,  236  * 
Stalactites,  173  * 
Stalagmites,  173  * 
Stamens,  276 


314      FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 


Standard  time,  30 
Starch  making,  269 

light  and  chlorophyll  necessary, 

270 
Stars,  14 

apparent  motion,  21 

brightness,  19 

change  in  position,  22 

distance,  19 

number,  14 

visible  all  the  year,  17 
Steam,  expansion,  79 

in  volcanic  eruptions,  228,  230, 
231 

pressure,  101 
Steel,  152 

Stems,  functions,  267 
Storms,  113 

cyclonic,  114 

local,  115 

tropical,  115 
Streams,  cause,  84 

temporary,  233 
Substance,  definition,  47 
Suction  pumps,  103,  104  * 
Suffocation,  141 
Sulphur,  151 

oxide,  152 
Sun,  22,  23 

apparent  motion,  24 

at  noon,  27 

eclipses,  42,  43  * 

source  of  energy,  287 
Sunrise,  23,  26  * 
Symbols,  chemical,  155 

Taurus,  15,  16,  21 

Telescopes,  43 

Temperature,    conditions    affecting, 

116 

Tenacity,  54 
Tendon,  294 
Terminal  moraine,  246 
Test,  definition,  158 
Thermometer,  71 

making,  71 

laboratory,  73  * 
Thunder,  115,  129 
Tides,  198,  199  * 
Time,  29,  30 

belts,  28  *,  30 

standard,  30 


Tin,  155 

Topographic  maps,  216,  222  * 

of  the  U.  S.,  221 

uses,  223 

Topography,  definition,  216 
Tornado,  112,  114* 
Torricelli's  experiment,  97 
Trade  winds,  113 
Translucent  medium,  121 
Transparent  medium,  121 
Tropic  of  Cancer,  25 

Uranus,  33,  35  *,  36 

Vacuum,  100 

Valley  contours,  220 

Vapors,  67 

Vega,  19 

Veins,  in  rock,  184 

of  minerals,  205 
Venus,  33,  34,  35  *,  36 
Venus  fly  trap,  255 
Vertebrates,  290 

study  of,  292 

Vesuvius  in  eruption,  229  * 
Viscosity,  81 
Vision,  121 
Volatility,  81 
Volcanoes,  228 

active,  228 

dormant,  228 

eruptions,  229,  230 

extinct,  228 
Volume,  49,  51  * 

unit  of,  63 

Waste  products  from  oxidation,  257 
Water,  carbonated,  94 

composition,  149 

excretion  by  plants,  269 

influence  on  climate,  78 

in  plants,  269 

natural,  83 

necessity  for,  259 

soda,  94 

Water  power,  84  * 
Water-worn  rock,  177  * 
Weather,  108 

Bureau,  108  * 

maps,  110*,  111 

records,  109 
Weathering,  233 


INDEX  315 


Weighing,  63  Work,  definition,  58 

Weight,  51,  61,  63  Wrought  iron,  152 
measurement  of,  51,  52  * 

Wells,  85,  86  *  Yolk  of  an  egg,  299 

Wheel  and  axle,  59,  60 

Winds,  112  Zenith,  20 

constant,  112  Zinc,  155 

trade,  113  Zones  of  light,  25 


LABOEATOEY  MANUAL 

TO  ACCOMPANY 

A  FIRST  YEAR  COURSE   IN 

GENERAL    SCIENCE 


BY 

CLARA  A.   PEASE 

OF  THE  HIGH  SCHOOL,   HARTFORD,    CONNECTICUT 


CHARLES  E.   MERRILL  COMPANY 

NEW  YORK  CHICAGO 


COPYRIGHT, 
BY  CHARLES  E.  MERRILL  CO. 


CONTENTS 


PAGE 

MATERIALS  NEEDED  FOR  THE  EXERCISES  IN  THE  LABORATORY.  5 
EXERCISE 

I.   THE  NORTHERN  SKY  IN  SEPTEMBER .    .  9 

II.   POSITION  OF  THE  SUN  AT  DIFFERENT  HOURS  OF  THE 

DAY 10 

III.  ORBITS  OF  SOME  OF  THE  PLANETS 11 

IV.  To  FIND  THE  VOLUME  OF  A  REGULAR  SOLID  ....  12 
V.   To  FIND  THE  WEIGHT  OF  A  BODY  BY  USE  OF  THE  PLAT- 
FORM BALANCE,  OR  TRIP  SCALE    ..........  13 

VI.   To  FIND  THE  DENSITY  OF  A  SOLID 13 

VII.   To  FIND  THE  CAPACITY  OF  A  BOTTLE  OR  FLASK  BY 

WEIGHING 14 

VIII.   To  FIND  THE  DENSITY  OF  A  LIQUID 15 

IX.   To  FIND  THE  SPECIFIC  GRAVITY  OF  A  SOLID  WHICH  is 

INSOLUBLE  IN  WATER 16 

X.   TESTING  THE  ACCURACY  OF  A  THERMOMETER  AT  THE 

FREEZING  POINT 17 

XI.   QUANTITY  OF  HEAT 18 

XII.   WEATHER  OBSERVATIONS  .    .    .    .  ' 19 

XIII.  VARIATIONS  IN  TEMPERATURE  SHOWN  BY  CURVES  .    .  20 

XIV.  THE  SIMPLE  ELECTRIC  CELL 21 

XV.   STUDY  OF  GAS  BURNERS  AND  FLAMES 23 

XVI.  HEATING  WITH  GAS  FLAMES 24 

XVII.   A  PRODUCT  OF  OXIDATION 24 

XVIII.   TESTS  FOR  ACID,  BASIC,  AND  NEUTRAL  SOLUTIONS.    .    .  25 

XIX.   STUDY  OF  ROCK  FORMATIONS 27 

XX.   REPRESENTING  ELEVATIONS  BY  CONTOURS 28 

XXI.  STUDY  OF  A  TOPOGRAPHIC  MAP 29 

3 


4  CONTENTS 

EXERCISE  PAGE 

XXII.   STUDY  OF  A  STREAM  AND  ITS  VALLEY 30 

XXIII.  THE  WATER  SUPPLY  OF  A  CITY  OR  TOWN 31 

XXIV.  THE  WHEAT  SEEDLING   ........ 32 

XXV.   STUDY  OF  THE  ROOTS  OF  A  PLANT 33 

XXVI.   STUDY  OF  THE  STEM  AND  LEAVES  OF  A  PLANT    ....  34 

XXVII.   ONE  FUNCTION  OF  LEAVES 35 

XXVIII.   TEST  FOR  FOOD  MATERIAL  IN  SEEDS 36 

XXIX.    STUDY  OF  A  FLOWER  .    ....    . 37 

XXX.    STUDY  OF  A  SEED    ..... 38 

XXXI.    STUDY  OF  A  FISH  40 


MATERIALS  NEEDED  FOR  THE  EXERCISES  IN 
THE  LABORATORY 

Below  is  given  a  list  of  materials  and  apparatus  needed  by  one 
pupil,  to  perform  all  the  experiments  and  exercises  in  the  MANUAL. 

Nearly  all  of  these  articles  are  possessed  by  a  school  which  has 
courses  in  physics  or  chemistry.  By  cooperation  and  a  little  planning 
to  avoid  conflict  as  to  time,  balances,  thermometers,  compasses,  and 
the  like  might  be  used  by  classes  in  different  branches  of  science.  It 
is  far  better,  however,  unless  the  work  is  all  done  in  the  same  labora- 
tory, that  each  department  should  have  and  should  care  for  its  own 
apparatus. 

Many  of  the  pieces  can  be  used  year  after  year.  Some  can  be 
obtained  from  local  dealers  or  from  the  homes  of  pupils. 

It  is  not  necessary  that  the  exercises  should  be  done  at  the  particular 
place  in  the  course  to  which  they  are  assigned.  If  it  is  impossible  to 
arrange  for  that,  it  is  better  that  the  exercise  should  follow  rather 
than  precede  the  study  of  a  subject. 

Drawing  compass. 

6-inch  ruler  divided  into  centimeters  on  one  edge,  inches 
on  the  other. 

Wooden  block,  cut  true  about  7X4X3  cm. 

Platform  balance. 

Set  of  weights  200,  100,  50,  20,  10,  5  g. 

Pieces  of  stone,  glass,  wax. 

Measuring  glass  (cylinder)  graduated  to  1  cu.  cm.,  capacity 
250  cu.  cm. 

Glass-stoppered  bottle,  holding  about  3  liquid  ounces. 

Battery  jar,  8  inches  in  diameter. 

Laboratory  thermometer  reading  to  1°  scale,  —  10°  to 
110°  C. 

2  pieces  of  brass,  iron,  or  zinc,  weight  about  200  and  400  g. 
May  be  cut  from  rods  1  inch  in  diameter. 

Coordinate  or  " graph"  paper. 

5 


6    MATERIALS  FOR  LABORATORY  EXERCISES 

Magnetic  compass. 
15-inch  insulated  copper  wire. 
2  binding  posts. 
Strip  of  zinc  and  of  copper. 
Bunsen  burner. 
Evaporating  dish. 
Combustion  spoon. 

Solutions   of   sulphuric   or   hydrochloric   acid,   ammonia, 
limewater,  iodine,  nitric  acid  (50  cu.  cm.  each). 
Common  salt. 

Strips  of  litmus  papers,  pink,  blue,  lilac. 
Dissected  cone  (base  3  inches). 
Sheet  of  topographic  map. 
Wheat  seeds;  dried  beans  or  peas. 
Young  plant  (can  be  raised  at  school). 
Low,  wide-mouthed  bottle. 
Flower. 
Fish. 


FIRST    YEAR   COURSE   IN 
GENERAL  SCIENCE 

LABORATORY  MANUAL 

The  Laboratory.  A  laboratory  is  a  place  in  which  to  do 
work  and  to  observe  and  record  the  results  and  effects  of 
things  done.  It  may  be  a  separate  room,  or  part  of  a  recita- 
tion room,  fitted  up  with  some  ordinary  flat-topped  tables 
and  chairs  or  stools  of  convenient  height.  It  is  desirable 
that  there  should  be  drawers  in  the  table  or  in  some  other 
part  of  the  room,  or  closed  shelves  where  apparatus  and 
materials  can  be  kept.  All  apparatus  should  be  returned  to 
its  place  in  good  order  by  the  pupil  who  has  used  it. 

Apparatus.  Everything  used  in  the  work  of  the  labora- 
tory is  apparatus,  whether  it  is  a  measuring  ruler,  a  ther- 
mometer, a  tumbler,  a  piece  of  wire,  or  a  bottle.  Every 
piece  of  apparatus  should  receive  care,  for  no  matter  how 
common  or  inexpensive  it  may  be,  if  it  is  not  in  condition  for 
use  when  needed  for  an  experiment  the  time  of  one  or  more 
pupils  is  lost  while  it  is  being  made  right  or  replaced. 

The  Laboratory  Notebook.  A  notebook  of  the  double- 
sheet,  loose-leaf  style  is  very  well  'adapted  to  laboratory 
use.  Each  sheet  may  be  laid  flat  on  the  table  during  the 
exercise,  may  be  handed  to  the  teacher  for  criticism,  and 
after  correction  and  approval  may  be  filed  away  in  the 
cover.  If  this  plan  is  followed,  there  is  no  danger  of  soiling 
or  injuring  previous  records  in  the  book  or  new  pages,  while 
in  the  laboratory. 

The  first  page  of  the  sheet  should  bear  at  the  top  — 
always  in  the  same  order  —  the  date  of   the   experiment, 

7 


8       FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

the  pupil's  .name,  and  the  number  of  the  exercise.  Below 
should  be  written  the  subject  of  the  exercise.  The  remainder 
of  the  page  may  be  occupied  by  an  outline  drawing  of  ap- 
paratus used.  On  the  second  page  should  be  copied  the 
directions  for  work,  and  below  them,  the  record  of  observa- 
tions. This  record  must  be  made  by  the  pupil  while  in- the 
laboratory,  not  afterward  from  memory.  Observations 
include  what  he  sees,  hears,  feels,  or  smells,  that  is,  what 
comes  to  him  through  the  senses.  The  pupil  should  be 
thinking  while  he  is  observing,  but  need  not  take  time  then 
to- tell  what  he  thinks.  That  can  be  done  later;  perhaps 
in  the  laboratory  after  his  desk  is  in  order,  perhaps  in  the 
classroom  the  next  day,  or  at  home.  He  need  not  then  try 
to  recall  what  happened,  because  he  has  the  record  of  ob- 
servations to  consult. 

Results.  The  results  of  the  experiment  may  be  given  in 
various  forms:  as  answers  to  questions  upon  the  work; 
or  the  working  of  a  problem  from  measurements  made  in 
the  laboratory;  or  an  explanation  based  upon  previous 
study  of  the  subject;  or,  better  still,  a  statement  of  what 
the  pupil  has  thought  about  the  experiment.  The  textbook 
may  be  consulted  in  answering  questions  on  the  "  result" 
page. 

It  is  best  to  write  the  results  on  the  third  page  opposite 
the  laboratory  record,  which  can  be  consulted  in  answering 
questions.  The  fourth  page  of  the  sheet  may  be  used  for 
observations  for  which  there  is  not  room  on  page  two,  for 
"  trial"  work  on  problems,  and  for  long  mathematical  work 
in  cases  where  only  the  indication  of  processes  is  needed  on 
the  "  result"  page. 

Composition.  Attention  should  be  given  to  penmanship 
and  English.  Illegible  and  inaccurate  reports  are  not  good 
work  in  science  any  more  than  in  language  or  mathematics. 
Avoid  the  use  of  /  as  the  subject.  Let  some  apparatus  or 
material  be  the  subject  and  use  its  name  instead  of  referring 


LABORATORY  MANUAL  9 

to  it  as  it.  Good  laboratory  work  is  worthy  of  the  best 
expression  the  pupil  can  give,  and  good  habits  of  work  are 
an  aid  to  advanced  study  in  any  subject. 

EXERCISE    I    (Textbook  §5) 

THE    NORTHERN    SKY    IN    SEPTEMBER 
(OR    ANY    OTHER    MONTH    SELECTED) 

APPARATUS:  Compasses,  hard  pencil,  sheet  of  notebook 
paper. 

NECESSARY  CoNDfriONs:  A  clear  evening  without  bright 
moonlight;  state  the  hour  of  observation. 

On  the  front  page  of  the  notebook  sheet  make  a  circle 
of  three-inch  radius.  At  the  center  place  *  and  mark  it 
P  (Pole  Star) .  Draw  a  dotted-line  vertical  diameter  through 
the  point  (*).  Draw  a  horizontal  line  across  the  page 
touching  the  lower  part  of  the  circle  at  the'  diameter's  in- 
tersection. Letter  the  horizontal  line  H  at  both  ends  and 
place  N  at  the  diameter. 

HH  is  a  part  of  the  northern  horizon,  N  is  the  north  point, 
and  the  line  PN  is  part  of  the  celestial  meridian.  If  the 
line  were  continued  upward  on  the  sky,  it  would  pass  through 
the  zenith  and  down  to  the  south  point  on  the  horizon. 

Within  the  circle,  place  the  groups  of  stars  you  observed 
in  the  northern  sky.  Indicate  the  brighter  stars  by  *,  the 
fainter  ones  by  X  .  Locate  carefully  the  position  of  each 
group  with  relation  to  the  Pole  Star  and  to  the  celestial 
meridian.  Estimate  carefully  the  space  occupied  by  each 
group. 

RESULTS 

1.  Write  neatly  the  name  of  each  constellation  under  the 
proper   group   on   your   map.     (Consult    the   textbook   on 
"  Stars  Visible  all  the  Year,"  p.  17.) 

2.  Which  group  as  a  whole  is  nearest  the  Pole  Star? 

3.  Which  group  is  highest  above  the  horizon? 


10     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

4.  Which  star  of  all  the  groups  is  farthest  from  the  Pole 
Star? 

5.  How  will  the  position  of  the  groups  have  changed  in 
six  hours? 

6.  Which  group  or  groups  will  then  be  east  of  the  meridian? 

7.  Through  what  points  of  earth  and  sky  does  the  celestial 
meridian  pass? 

8.  What  meridian  of  the  earth  lies  directly  under  the 
celestial  meridian,  that  is,  passes  through  the  place  where 
you  are? 

EXERCISE    II    (Textbook  §  18) 

POSITION  OF  THE  SUN  AT  DIFFERENT  HOURS 
OF  THE  DAY 

APPARATUS:  Hard,  sharp  pencil;  needle  about  No.  5 
or  No.  6;  sheet  of  notebook  paper. 

NECESSARY  CONDITIONS:  Sunshine  and  access  to  a 
south  exposure. 

DIRECTIONS  FOR  WORK:  Put  N,  S,  E,  W,  at  the  margins 
of  the  second  page  as  on  a  map.  Place  the  sheet  of  note- 
book paper  on  a  south  windowsill,  or  on  a  south  piazza, 
floor  with  the  lower  edge  of  the  paper  toward  the  south  and 
in  an  east-west  direction.  Stick  a  long  needle  or  pin  into 
the  paper  in  a  vertical  position  near  the  south  edge,  and 
with  a  sharp  pin  or  needle  prick  a  hole  at  the  end  of  the 
shadow  it  casts: 

(a)  two  hours  before  noon;  (d)  one  hour  after  noon; 
(6)  one  hour  before  noon;  (e)  two  hours  after  noon. 
(c)  at  noon; 

Connect  each  of  these  points  with  the  point  made  by 
the  large  needle,  using  a  light  ruled  pencil  line. 

RESULTS 

1.  State  the  direction  of  the  first  shadow  from  the  pin. 

2.  State  the  direction  of  the  second  shadow  from  the  pin. 


LABORATORY  MANUAL  11 

3.  State  the  direction  of  the  noon  shadow  from  the  pin. 

4.  State  the  direction  of  the  afternoon  shadows  from  the 
pin. 

5.  In  what  direction  would  you  look  for  the  sun  at  noon? 

6.  Before  noon? 

7.  What  differences  in  the  length   of  shadows   do  you 
observe? 

8.  Were  any  two  shadows  nearly  equal  in  length?     Which 
ones? 

9.  Give   directions   for   making   a   sundial   which    "tells 
time"  by  the  direction  of  sun  shadows. 

EXERCISE    III    (Textbook  §  26) 
ORBITS  OF  SOME  OF  THE   PLANETS 

APPARATUS:     Hard  pencil,  ruler,  compasses. 

DIRECTIONS  FOR  WORK:  In  the  middle  of  the  space 
below  [on  p.  2  of  notebook  sheet],  place  the  letter  S.  Con- 
struct three  circles  (with  the  same  center,  S)  having  a 
radius  of  J  in.,  f  in.,  and  2|  in.,  respectively.  On  the  left, 
place  V  (Venus)  on  the  smallest  circle,  E  (Earth)  on  the 
second,  J  (Jupiter)  on  the  largest,  all  in  the  same  line  from 
S.  Let  the  circles  represent  the  orbits  or  paths  of  one 
revolution  of  the  earth  and  these  two  other  planets  about 
the  sun.  (NOTE.  The  orbits  of  the  planets  are  ellipses,  not 
circles,  but  it  is  not  possible  to  represent  their  form  correctly 
in  small  drawings.) 

RESULTS 

1.  What  fraction  of  its  orbit  represents  the  earth's  journey 
for  six  months? 

2.  How  many  degrees  does  the  earth  pass  over  in  that 
time? 

3.  How  long  does  it  take  the  earth  to  pass  over  90°? 

4.  Hpw  long  does  it  take  Venus? 


12     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

5.  How  long  does  it  take  Jupiter? 

6.  Compare  the  distances  in  miles  traversed  by  the  three 
planets  in  advancing  90°  each. 

7.  (a)  If  the  direction  from  E  to  S  is  westward,  in  what 
direction  is  J  from  Ef     (6)  In  what  part  of  the  sky  would 
Jupiter  be  at  sunset? 

8.  (a)  In  what  part  of  the  sky  would  Venus  be  at  sunset? 
(b)  Would  it  be  likely  to  be  visible?     Why? 

9.  Place    X  at  the  point  on  its  orbit  where  each  planet 
would  be  three  months  after  the  positions  indicated  in  your 
diagram. 

EXERCISE    IV    (Textbook  §  47) 

TO  FIND  THE  VOLUME   OF  A  REGULAR  SOLID 

APPARATUS:     Centimeter  rule,  rectangular  wooden  block. 

DIRECTIONS  FOR  WORK:  Measure  the  length  of  the 
block  along  the  grain  on  the  four  sides.  Read  and  record 
each  length  to  .1  cm.  Measure  and  record  the  width  and 
thickness  in  the  same  way. 

Kind  of  wood Number  of  block 

Length  Width  Thickness 

(1)      cm.  ' cm.  cm. 

(2) cm.  .  . cm.  cm. 

(3)      cm.  cm.  cm. 

(4)      cm.  cm.  cm. 

Sum cm.  cm.  cm. 

RESULTS 

1.  Calculate  and  record   the  average  length,  width,  and 
thickness  to  the  nearest  .1  cm. 

2.  Find  the  volume  of  the  block  to  the  nearest  centimeter. 
NOTE.     If  the  average  width  should  work  out  4.125  cm., 

record  it  as  4.1  cm.;  if  4.175  cm.,  record  it  as  4.2  cm.  Since 
we  do  not  measure  more  closely  than  to  .1  cm.,  it  is  un- 
reasonable to  give  the  result  in  hundredths  or  in  thousandths. 


LABORATORY  MANUAL  13 

EXERCISE    V   (Textbook  §  64) 

TO  FIND  THE   WEIGHT  OF  A  BODY  BY  USE   OF 
THE   PLATFORM   BALANCE,    OR   TRIP  SCALE 

APPARATUS:  Platform  balance,  bodies  to  be  weighed 
(blocks  of  wood  used  in  previous  experiment,  pieces  of 
stone  or  metal). 

DIRECTIONS  FOR  WORK:  Place  the  body  to  be  weighed 
upon  the  left-hand  platform.  Have  the  sliding  weight  at 
the  0  point  of  the  scale.  Upon  the  right-hand  platform, 
place  weights  that  will  nearly  balance  the  body.  Move 
the  sliding  weight  to  such  a  position  that  the  platforms  are 
at  the  same  level.  Record  the  weight  in  grams  to  .1  g. 

Platform  balance,  number 

Body                         No.                            Weight 
-g- 


RESULTS 

1.  What   change   in   the   apparatus   occurred   when   the 
block  was  placed  on  the  left  platform?     Explain. 

2.  When  the  " weighing"  is  accomplished,  what  keeps  the 
platforms  at  the  same  level? 

3.  Describe  some  other  kind  of  balance. 

4.  What  force  is  measured  in  weighing  a  body? 

EXERCISE    VI    (Textbook  §  66) 
TO  FIND  THE  DENSITY  OF  A  SOLID 

APPARATUS:  Balance,  jar  of  water,  metric  measure, 
various  solid  bodies. 

DIRECTIONS  FOR  WORK:  If  the  body  is  a  regular  solid, 
find  its  volume  by  measurement  (Ex.  IV),  and  its  weight 
by  use  of  the  balance  (Ex.  V).  If  the  body  is  irregular  and 


14     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

insoluble,  find  its  volume  by  means  of  a  measuring  glass 
(see  Textbook  §66). 

Name  Volume  Weight 

.  .cu.  cm.'  .  .g. 


RESULTS 

(Indicate  the  operation  by  which  your  answers  are  ob- 
tained.) 

1.  If  36  cu.  cm.  of  matter  weigh  72  g.,  what  is  its  weight 
per  cu.  cm.? 

2.  Find  the  weight  per  cu.  cm.  of  each  solid  used.     (Do 
the  figuring  on  p.  4  and  arrange  the  results  in  the  tabular 
form  below.) 

Body  Volume  Weight  Density 

cu.  cm. g.  g.   per   cu.   cm. 


EXERCISE    VII    (Textbook  §  67) 

TO  FIND  THE  CAPACITY  OF  A  BOTTLE  OR  FLASK 
BY  WEIGHING 

APPARATUS:    Balances,    small    bottle    having    a   ground 
glass  stopper,  a  jar  of  water. 
DIRECTIONS  FOR  WORK: 

(1)  Weigh  to  .1  g.  a  dry,  empty  bottle  with  its  stopper. 
Record  the  number  of  the  bottle  and  its  weight. 

(2)  Hold  the  bottle  in  a  jar  of  water  until  it  is  filled,  and 
while  it  is  under  water,  insert  the  stopper  firmly.     Wipe  the 
outside,  weigh  again,  and  record. 

Weight  of  empty  bottle  No g. 

Weight  of  bottle  full  of  water g. 


LABORATORY  MANUAL  15 

RESULTS 

1.  How  many  grams  of  water  does  the  bottle  hold? 

2.  What  is  the  weight  of  1  cu.  cm.  of  water? 

3.  How  many  cu.  cm.  of  water  will  the  bottle  hold? 

4.  How  many  cu.  cm.  of  molasses  will  the  bottle  hold? 

5.  Give  directions  for  finding  the  capacity  of  a  pitcher 
in  metric  units,  by  this  method. 

6.  How  could  you  find  the  capacity  of  a  pitcher  in  English 
units  by  this  method? 

7.  State  the  difference  in  meaning  between  volume  and 
capacity. 

EXERCISE    VIII    (Textbook  §  67) 
TO  FIND  THE   DENSITY  OF  A  LIQUID 

APPARATUS:  Balances;  bottle;  various  liquids,  such  as 
alcohol,  kerosene,  strong  solution  of  blue  vitriol,  and  sal 
ammoniac. 

DIRECTIONS  FOR  WORK:  Use  a  bottle  whose  weight  and 
capacity  have  been  determined  by  the  method  used  in 
Ex.  VII;  fill  it  with  a  given  liquid  and  weigh. 

(1)  Weight  of  bottle  empty  (from  Ex.  VII)  g. 

(2)  Capacity  of  the  bottle  (from  Ex.  VII)    cu.  cm. 

(3)  Weight  of  bottle  filled  with g. 

(4)  Weight  of  bottle  filled  with ! g. 

(5)  Weight  of  bottle  filled  with g. 

RESULTS 

Calculate  and  record  in  tabular  form  the  density  of  each 
liquid  used. 

Name  of  Liquid                Volume          Weight                    Density 
cu.  cm g.  g.  per  cu.  cm. 


16     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

EXERCISE    IX    (Textbook  §  68) 

TO  FIND  THE  SPECIFIC   GRAVITY  OF  A  SOLID 
WHICH   IS  INSOLUBLE  IN   WATER 

APPARATUS:  Balance,  sink  or  jar  containing  water, 
thread,  solids  (such  as  pieces  of  stone  or  coal),  glass  stopper, 
cake  of  wax. 

DIRECTIONS  FOR  WORK: 

(1)  Weigh  the  solid  in  air. 

(2)  Weigh  the  solid  in  water.     To  do  this,  tie  a  thread 
around  the  object  and  suspend  it  from  the  balance  in  a  jar 
of  water.     Do  not  allow  the  object  to  touch  the  side  or 
bottom  of  the  jar  nor  to  come  to  the  surface  of  the  water. 

Name  of  Solid  Wt.  in  Air  Wt.  in  Water 

g-  • g- 

RESULTS 

1.  Do  the  solids  weigh  more  in  air  or  in  water? 

2.  How  much  was  the  difference  in  weight,  in  the  case 
of  the  first  body  weighed? 

3.  What  change  occurred  in  the  level  of  the  water  when 
the  solid  was  immersed?     Why? 

4.  If  the  volume  of  a  solid  used  was  50  cu.  cm.,  how  many 
cu.  cm.  of  water  did  it  displace  when  it  was  immersed  in 
water? 

5.  What  is  the  weight,  in  grams,  of  the  water  displaced? 
Why? 

6.  What  is  the  relation  between  the  weight  of  the  solid  in 
air  and  the  loss  of  weight  in  water?     Express  as  a  fraction. 

7.  Compute  to  two  decimal  places  these  ratios  and  thus  get 
the  specific  gravity  of  each  solid. 

Name  of  Solid        Ratio  between  Weight       Specific  Gravity 
and  Loss  in  Water 


LABORATORY  MANUAL  17 

EXERCISE    X    (Textbook  §  75) 

TESTING  THE  ACCURACY  OF  A  THERMOMETER 
AT  THE  FREEZING   POINT 

APPARATUS:  Broken  ice  and  water  in  a  tumbler;  a 
laboratory  Centigrade  thermometer;  a  common  Fahrenheit 
thermometer  brought  from  home. 

DIRECTIONS  FOR  WORK: 

(1)  Make  a  drawing  of  the  laboratory  thermometer,  on 
the  first  page  of  notebook  paper. 

(2)  Place  the  bulb  of  the  thermometer  in  the  ice  and 
water;  keep  it  there  until  the  mercury  in  the  tube  is  station- 
ary, read  to  .5  of  a  degree,  and  record  in  degrees  C.     If 
below  0°,  record  with  the  minus  sign,  as  —  1°  C.     Dry  and 
return  the  thermometer  to  its  case. 

(3)  Place  a  common  thermometer  in  the  ice  and  water  as 
directed  in  Case  2,     (If  it  has  a  wooden  or  metal  frame,  it 
will  not  be  injured.)     Record  the  reading  in  degrees  F.  to 
the  nearest  whole  degree. 

Reading  of  the  laboratory  thermometer *. °C. 

Reading  of  the  common  thermometer         °F. 

RESULTS 

1.  What  difference  did  you  note  between  your  thermom- 
eter and  the  laboratory  thermometer  — 

(a)  in  regard  to  construction? 
(6)  in  regard  to  scale? 

(c)  in  regard  to  range  of  temperature  (that  is,  the  differ- 
ence between  the  lowest  and  highest  readings)? 

(d)  Which  of  these  differences  affect  its  usefulness  for 
ordinary  purposes?     Why? 

2.  What  is  the  temperature  of  melting  ice?     °C.? 


18     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

3.  Was  the  laboratory  thermometer  accurate  as  judged 
by  your  answers  to  (2)? 

4.  Was  yaur  own  thermometer  accurate,  judged  in  the 
same  way? 

5.  Tell  how  the  accuracy  of  a  thermometer  at  the  boiling 
point  might  be  tested. 

EXERCISE    XI    (Textbook  §  83) 
QUANTITY  OF  HEAT 

APPARATUS:  Pieces  of  brass  or  iron  of  about  the  same 
weight;  some  pieces  about  twice  as  heavy;  thermometer; 
tumbler  of  water  which  has  been  standing  in  the  room  for 
some  time;  kettle  of  hot  water  (about  boiling).  The  metals 
should  have  a  thread  tied  around  them  so  that  they  can  be 
lifted  from  the  hot  water. 

DIRECTIONS  FOR  WORK  : 

(1)  Place   the  small   metal  objects    in  hot   water   until 
thoroughly  heated.     Fill  the  tumbler  f  full  with  water  at 
room  temperature.     Observe  and  record  to  .5°,  in  the  table 
below,  the  temperature  of  water  in  the  tumbler.     Quickly 
transfer  one  hot  metal  to  the  water  in  the  tumbler,  and 
while   stirring  the  water   carefully  with  the  thermometer, 
read  the  highest  temperature  indicated. 

(2)  Repeat  with  fresh  water  at  room  temperature  in  the 
tumbler.     This  time  place  a  larger  body  of  the  same  metal, 
or  two  of  the  same  size  as  in  (1)  in  the  water.     Record  data 
in  tables  below. 


Temp,  of  water 
before  adding 
hot  metal 
1.  °C. 
2.   .                ..°C. 

Temp,  of  water 
after  adding 
hot  metal 
°C. 
.  .°C. 

Difference  between 
temperatures 

°C. 
..°C. 

LABORATORY  MANUAL  19 

RESULTS 

1.  Did  the  greater  change  in  temperature  take  place  when 
the  large  or  small  mass  was  used? 

2.  Which  gave  the  greater  quantity  of  heat  when  placed 
in  water,  the  small  or  the  large  mass? 

3.  If  the  tumbler  contained  400  g.  of  water  in  Case  2,  how 
many  calories  did  the  water  absorb  from  the  heated  metal, 
as  shown  by  your  observation? 

4.  A  man  wishes  to  heat  his  house  with  steam  at  212°  F., 
and  can  get  two  sizes  of  radiators.     If  he  wishes  to  keep  the 
house  as  warm  as  possible,  should  he  buy  the  large  or  the 
small  radiators?     Why? 

5.  Why  are  hot-water  radiators  necessarily  larger  than 
steam  radiators? 

EXERCISE    XII    (Textbook  §  115) 
WEATHER  OBSERVATIONS 

APPARATUS:    A  thermometer;  ruler. 

CONDITIONS  NECESSARY:  A  thermometer  placed  out  of 
doors  where  the  sun  does  not  shine  upon  it  at  any  time, 
and  not  in  contact  with  the  wall  of  the  house. 

DIRECTIONS  FOR  WORK  :  Prepare  a  page  of  your  notebook 
in  six  vertical  columns,  the  first  three  narrower  than  the 
others,  with  the  following  headings,  and  in  the  proper  column 
make  your  record. 

Date     Hour     Tern.  Sky  Wind  Rain 

Under  sky,  report  clear,  if  blue  with  here  and  there  white 
clouds;  cloudy,  if  nearly  the  whole  sky  is  covered;  overcast, 
if  of  one  uniform  gray  with  sun  invisible. 

Under  wind,  give  the  direction;  and  light,  variable, 
strong,  or  steady  as  case  may  be. 

Rain,  light  or  heavy. 


20     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

Make  three  observations  at  least  three  hours  apart  each 
day  for  a  week.  If  you  have  access  to  a  barometer,  give  its 
reading  also. 

RESULTS    • 

State  the  relation  (if  any)  shown  by  the  record  between  - 

1.  The  temperature  and  the  time  of  day. 

2.  The  condition  of  the  sky  and  the  wind. 

3.  The  condition  of  the  sky  and  rain. 

4.  The  direction  of  the  wind  and  rain. 

5.  Why  is  it  necessary  that  the  thermometer  should  not 
be  in  contact  with  the  wall  of  a  building? 

EXERCISE    XIII    (Textbook  §  127) 
VARIATIONS  IN  TEMPERATURE  SHOWN   BY  CURVES 

APPARATUS:  A  thermometer  hung  out  of  doors  not  in 
contact  with  a  warm  wall  of  a  house,  and  not  in  the  sun- 
shine; a  sheet  of  coordinate  paper  at  least  16  X  20  cm. 
ruled  in  2  mm.  spaces,  with  heavy  rulings  1  cm.  apart. 
(This  can  be  procured  from  dealers  in  draughtsmen's 
supplies.) 

DIRECTIONS  FOR  WORK: 

(1)  Prepare  the  paper  by  dating  the  heavy  vertical  lines 
with  15  consecutive  dates,  placing  at  the  left  the  date  of 
first  observation.     Place  the  number  of  degrees  at  the  left 
end  of  the  heavy  horizontal  lines.     If  in  the  winter  season 
north  of  the  40°  latitude,  let  -20°  F.  be  the  lowest;  if  south 
of  40°,  let  10°  F.  be  the  lowest;  and  number  up  by  succes- 
sive fives.     If  in  summer,  begin  with  30°  at  the  lowest  line. 

(2)  Read    the   thermometer  at  what   you   consider    the 
warmest  part  of  the  day,  and  make  a  dot  at  the  intersection 
of  the  date  line  and  the  line  of  the  degree  read.     Place 
another  dot  on  the  same  date  line  at  the  line  of  lowest  tem- 
perature which  you  can  observe  for  that  date  (probably  in 
evening).     Repeat  for  each  date  for  two  weeks  or  more. 


LABORATORY  MANUAL  21 

Connect  by  light  straight  lines  the  successive  points 
indicating  maximum  temperatures,  and  by  another  set  of 
lines  the  minimum  temperatures. 

The  official  record  of  maximum  and  minimum  tempera- 
tures may  be  obtained  on  application  to  the  local  office  of 
the  Weather  Bureau.  If  secured,  make  another  set  of 
records  and  lines,  and  compare  with  your  records. 

RESULTS 

NOTE.  Such  a  series  of  lines  as  you  have  made  is  called 
by  scientists  a  curve.  The  range  of  temperature  is  the  differ- 
ence between  the  highest  and  lowest  temperatures  of  a 
period. 

1.  What  is  the  highest  reading  recorded  by  the  tempera- 
ture curve?    The  lowest? 

2.  Are  the  variations  from  day  to  day  alike? 

3.  What  was  the  range  of  temperature  for  the  period  of 
observations? 

4.  What  was  the  greatest  daily  range?     Give  date. 

5.  What  was  the  least  daily  range?     Give  date. 

6.  What   was   the   highest    average   temperature?     Give 
date. 

7.  What    was    the    lowest    average    temperature?     Give 
date. 

EXERCISE    XIV    (Textbook  §  142) 
THE   SIMPLE  ELECTRIC   CELL 

APPARATUS:  A  small  strip  of  copper,  a  strip  of  zinc, 
insulated  copper  wire,  binding  screws,  compass,  tumbler  of 
water  containing  a  little  acid  (about  1  part  acid  to  12  parts 
water) . 

DIRECTIONS  FOR  WORK:  Caution:  Sulphuric  acid,  which 
is  heavier  than  water,  should  always  be  poured  into  the 
water;  never  pour  the  water  upon  the  acid.  In  the  latter 


22     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

case,  steam  is  formed,  and  it  is  liable  to  push  out  and  scatter 
the  mixture.  Even  weak  acid  is  injurious  to  the  skin  and 
clothing. 

Record  what  happens  in  each  of  the  following  cases.  If 
no  visible  action  occurs  at  once,  continue  to  watch  closely 
for  half  a  minute.  Note  differences  in  degree  as  well  as  in 
kind  of  changes. 

Place  in  the  add  solution  Observation 

1.  A  strip  of  copper  alone. 

2.  A  strip  of  zinc  alone. 

3.  Copper  and  zinc  together  with- 

out contact  outside  or  in  the 
acid. 

4.  Copper  and  zinc  together  con- 

nected by  a  wire  outside. 

5.  Remove  the  metals  from   the 

liquid;  wind  the  wire  twice 
around  a  compass  from  N  to 
S.  Note  any  effect  on  the 
needle. 

6.  With  the  compass  in  the  coiled 

wire,  replace  the  metal  strips 
in  the  liquid  and  observe  the 
position  of  the  needle. 

RESULTS 

1.  Upon  which  of  the  two  metals  used  does  the  weak  acid 
act  more  readily? 

2.  What  effect  upon  the  position  of  a  magnetic  needle  is 
produced  by  an  electric  current  passing  around  the  needle? 

3.  How  do  you  know  that  it  was  the  current  and  not  the 
wire  that  produced  the  effect? 

4.  Name,  in  order,  all  the  substances  which  made  the 
circuit  for  the  current  in  Case  6. 

6.  Name  a  case  in  which  the  circuit  was  broken. 


LABORATORY  MANUAL  23 

EXERCISE   XV    (Textbook  §  155) 
STUDY  OF  GAS  BURNERS  AND  FLAMES 

Gas  flames  are  of  two  kinds,  luminous  (light-giving)  and 
non-luminous.  A  laboratory  burner  is  called  a  Bunsen 
burner  (from  the  name  of  the  German  chemist  who  invented 
it).  Use  these  terms  whenever  appropriate  in  this  exercise. 

APPARATUS:  A  Bunsen  burner,  a  porcelain  evaporating 
dish,  a  laboratory  thermometer. 

DIRECTIONS  FOR  WORK: 

(1)  Examine   the  Bunsen  burner  carefully  and   write   a 
brief  description  of  it.     Make  a  drawing  of  it  on  the  first 
page. 

(2)  Adjust  the  brass  ring  at  the  base  of  the  burner  so  that 
the  holes  are  covered.     Turn  on  the  gas  full  head,  and  then 
bring  a  lighted  match  over  the  burner.     Turn  the  stopcock 
until  the  flame  is  about  two  inches  long,  and  describe  it. 

(3)  Hold  the  outside  of  an  evaporating  dish  in  the  upper 
part  of  flame  for  a  few  seconds  and  describe  any  change  in 
the  appearance  of  the  dish. 

(4)  Turn  the  brass  ring  at  the  base  of  burner  until  the 
flame   is   entirely   changed   in   appearance.     Describe   this 
flame. 

(5)  Hold  a  clean  evaporating  dish  in  the  flame  for  a  few 
seconds  and  record  observations. 

RESULTS 

1.  What  kind  of  flame  has  an  ordinary  gas  burner? 

2.  How  can  a  similar  flame  be  made  with  a  Bunsen  burner? 

3.  What  kind  of  flame  has  a  gas  stove  or  range? 

4.  How  can  a  similar  flame  be  made  with  a  Bunsen  burner? 

5.  Which  is  the  cleaner  of  the  two  flames,  the  one  in  Case 
2  or  Case  4? 

6.  Give  a  name  for  the  coating  formed  on  the  evaporating 
dish. 


24     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

EXERCISE    XVI    (Textbook  §  155) 
HEATING    WITH    GAS    FLAMES 

APPARATUS:     Bunsen  burner,   thermometer,   evaporating 
dish. 

DIRECTIONS  FOR  WORK: 

(1)  Put  into  a  porcelain  dish  100  cu.  cm.  of  water,  after 
noting  its  temperature;   record  its  temperature  after  heating 
5  min.  with  a  luminous  flame.     (Stir  the  water  with  the 
thermometer  while  -heating  and  keep  the  bulb  of  the  ther- 
mometer in  the  water  until  after  reading  and  recording  the 
temperature.) 

(2)  With  fresh  water,  repeat  the  work  of  Case  1,  using  a 
non-luminous  flame. 

Case  1.     Temp,  of  water  at  start Temp,  at  end 

Case  2.     Temp,  of  water  at  start Temp,  at  end 


RESULTS 

1.  What  kind  of  flame  is  best  for  cooking  purposes?    Why? 

2.  Why  does  the  flame  give  more  heat  if  air  can  enter  the 
gas  tube  and  mix  with  the  gas  before  burning? 

3.  The  lampblack  deposited  on  the  porcelain  comes  from 
the  flame.     Is  its  color  the  same  while  in  the  flame?     Why? 

4.  From  this,  give  an  explanation  of  light  from  a  flame. 

EXERCISE    XVII    (Textbook  §  164) 
A  PRODUCT  OF   OXIDATION 

APPARATUS:  A  piece  of  charcoal  (which  is  nearly  pure 
carbon),  a  combustion  spoon,  a  bottle  of  air,  limewater,  a 
beaker  or  tumbler. 

DIRECTIONS  FOR  WORK:  If  no  change  is  observed  in 
the  following  work,  the  record  should  be  "no  apparent 
change." 


LABORATORY  MANUAL  25 

(1)  Put  a  little  limewater  into  a  clean  empty  bottle  and 
shake  it. 

(2)  Place  a  piece  of  charcoal  on  a  combustion  spoon  and 
hold  in  a  gas  flame  until  it  glows  (i.e.  burns  without  flame). 
Lower  it  then  into  a  bottle  of  air  and  keep  it  there  as  long  as 
it  glows.     After  removing  the  spoon  and  coal,  pour  into  the 
bottle  a  little  limewater;  cover  the  mouth  of  the  bottle  and 
shake  it.     Describe  any  change  in  the  limewater. 

(3)  By  means  of  a  glass  tube,  breathe  through  some  fresh 
limewater  in  a  beaker.     Describe  the  effect. 

RESULTS 

1.  What  compound  is  made  when  carbon  is  burned  in  air 
or  in  oxygen? 

2.  Give  two  other  names  for  " burning." 

3.  What  physical  effect  did  the  burning  of  the  charcoal 
have  on  the  air  in  the  bottle? 

4.  How  did  the  gas  made  by  burning  carbon  affect  the 
appearance  of  the  limewater? 

5.  In  what  other  case  was  a  similar  effect  produced? 

6.  What  proof  did  your  experiment  give  that  exhaled 
air  differs  from  air  inhaled? 

7.  What  chemical  process  must  occur  in  the  body  to  cause 
this  difference? 

8.  Why  is  the  living  body  warmer  than  the  outside  air? 


EXERCISE    XVIII    (Textbook  §  181) 
TESTS  FOR  ACID,   BASIC,   AND  NEUTRAL  SOLUTIONS 

MATERIALS:  Solution  of  an  acid  (sulphuric),  a  base 
(ammonium  hydroxide),  and  a  neutral  substance  (common 
salt),  a  glass  rod,  narrow  strips  of  pink,  blue,  and  lilac  litmus 
papers. 


26     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

DIRECTIONS  FOR  WORK: 

(1)  Pour  25  cu.  cm.  of  water  into  an  evaporating  dish  and 
add  a  few  drops  of  an  acid.     Place  the  three  litmus  papers 
on  a  clean  paper.     With  a  clean  rod,  put  a  drop  of  acid  on 
one  end  of  each  paper.     Record  any  or  no  change  of  color 
observed,  in  the  table  below. 

(2)  Wash  the  dish  and  rod  clean  and  dry  them.     Pour 
25  cu.  cm.  of  water  into  a  dish  and  add  a  few  drops  of  am- 
monium hydroxide   (ammonia  solution).      Put  a  drop   on 
each  paper  where  it  will  not  touch  the  spot  made  in  Case  1. 
Record  change  in  the  table  below. 

(3)  Make  the  apparatus  clean  and  repeat  the  above  tests 
with  a  solution  of  common  salt,  a  neutral  substance. 

(4)  Take  home  2  sq.  in.  of  lilac  paper  (provided  by  the 
teacher)  and  test  as  many  other  solutions  as  possible. 

Litmus  papers  Blue                       Pink                     Lilac 

Acid  Solution  

Basic  

Neutral      "  

Soap  

Molasses    '  

Vinegar       "  ....'. 

Milk  (sweet)  

"       (sour)  

Sugar  solution  

Starch        "  

Baking  soda  "  


RESULTS 

1.  Describe   the   behavior   of   each   of  the   three   litmus 
papers  with  each  of  the  first  three  solutions. 

2.  Which  is  the  best  paper  to  use  if  only  one  can  be  had? 
Why? 


LABORATORY  MANUAL  27 

3.  Arrange  a  table  to  show  the  character  of  all  the  sub- 
stances tested. 

Add  Basic  Neutral 


EXERCISE    XIX    (Textbook  §  208) 

STUDY  OF  ROCK  FORMATIONS 

PLACE:  A  hill  or  mountain  where  the  rocks  are  exposed; 
or  a  cut  made  through  a  hill  for  a  road;  or  rocks  on  sea, 
lake,  or  river  shore. 

Upon  an  extra  sheet  of  paper  take  notes  (to  be  trans- 
ferred neatly  to  the  notebook  and  used  in  writing  results) 
on  each  of  the  topics  given  below: 

1.  The  extent  of  the  rock  exposed. 

2.  The  position  of  the  rock. 

3.  The  color  of  the  rock. 

4.  The  hardness  of  the  rock. 

5.  Difference  in  color  of  a  freshly  broken  and  a  long 
exposed  rock. 

6.  The  direction  of  any  cracks  or  natural  breaks. 

7.  Division  of  the  rocks  into  horizontal  layers. 

8.  Presence  of  crystals  or  crystalline  formations. 

9.  Signs  of  action  of  air  or  water,  past  or  present. 

Tell  where  you  found  any  of  the  following  rocks  or  min- 
erals: sandstone,  shale,  limestone,  'conglomerate,  granite, 
trap,  quartz,  feldspar,  mica. 

State  the  length  of  time  spent  in  studying  the  rocks  and 
making  notes. 

RESULTS 

Write,  in  ink,  in  well  chosen  words,  a  two-page  descrip- 
tion of  the  rocks  you  studied,  using  your  notes  on  every 
topic  given  above.  The  order  of  the  topics  need  not  neces- 
sarily be  followed. 


28     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

EXERCISE    XX    (Textbook  §  239) 
REPRESENTING  ELEVATIONS  BY  CONTOURS 

MATERIALS  :  A  wooden  cone  cut  into  three  or  more  hori- 
zontal sections,  or  a  turnip,  large  carrot,  or  parsnip  of  some- 
what conical  shape;  a  knife;  a  sharp  pencil;  a  hatpin  or 
long  pin;  a  measuring  ruler;  an  extra  sheet  of  paper. 

DIRECTIONS  FOR  WORK:  Remove  the  small  tapering  end 
from  the  body  selected.  Cut  the  object  across  at  its  largest 
part  at  right  angles  to  its  length,  so  as  to  give  it  a  flat  base. 

(1)  Take  the  part  which  is  nearest  to  a  cone  in  shape  and 
measure  its  height;   the  length  and  width  of  its  base. 

(2)  Pass  a  long  pin,  or  wire,  through  the  body  from  top  to 
bottom,  letting  the  point  come  through  the  base.     Place 
the  body  on  a  sheet  of  paper  (not  notebook  paper)  and 
draw  its  profile,  natural  size. 

(3)  Draw  a  line  upon  the  paper  completely  around  the 
base.     This  is  the  contour  line  of  the  base.     Press  the  pin 
enough  to  make  it  prick  the  paper. 

(4)  Remove  the  object,  draw  out  the  pin  a  little  way,  and 
cut  off  from  the  bottom  of  the  object  about  J  of  its  height. 
Replace  upon  the  paper,  so  that  the  pin  will  prick  the  same 
place  as  before.     Draw  the  contour  line  of  the  new  base. 

(5)  Repeat  until  the  object  is  in  four  pieces.     Draw  the 
outline  of  each  base  and  at  last  the  outline  of  the  top. 

(6)  Replace  the  sections  and  show  the  place  of  each  cut  by 
dotted  lines  on  the  profile  (Case  2  above).     Number  the 
lines,  beginning  with  0,  the  base.     Letter  the  several  base 
outlines,  beginning  with  a,  the  first. 

RESULTS 

Consider  the  body  in  position  as  in  Case  6. 
1.  What  is  the  elevation  of  the  first  section  line  above 
the  base?     (This  is  the  contour  interval.) 


LABORATORY  MANUAL  29 

2.  The  elevation  of  the  third  section  line? 

3.  By  what  contour  lines  are  these  elevations  represented? 

4.  What  is  the  elevation  of  contour  line  a?    Contour  line  cf 

5.  Compare  the  area  of  the  base  of  the  object  with  that  of 
the  other  sections. 

6.  Which  of  your  drawings  represents  this  comparison? 

7.  If  an  insect  crawled  by  the  shortest  line  up  the  side  of 
the  object  you  have  studied,  what  line  on  the  profile  would 
represent  his  path? 

8.  How  would  his  path  be  represented  on  the  contour 
lines? 

EXERCISE    XXI    (Textbook  §  243) 
STUDY  OF  A  TOPOGRAPHIC   MAP 

MATERIALS  :  A  sheet  of  a  topographic  map  of  the  region 
in  which  you  live.  (Such  maps  are  made  by  the  U.  S. 
Geological  Survey  in  connection  with  the  state.  They  can 
be  procured  at  ten  cents  each,  cash  or  money  order,  from 
the  Director  U.  S.  G.  S.,  Washington,  D.  C.) 

DIRECTIONS  FOR  WORK:  Select  a  portion  of  the  map  in 
which  there  are  streams,  highways,  railroads,  and  two 
towns  a  few  miles  apart.  (Choose  the  portion  that  is  most 
familiar  to  you.)  Note  the  horizontal  scale  as  indicated  at 
the  bottom  of  the  map. 

(1)  What  is  the  meaning  of  white  areas  on  a  topographic 
map? 

(2)  What  is  the  meaning  of  few  contour  lines  to  the  inch? 

(3)  How  would  you  describe  a  region  where  contour  lines 
were  near  together? 

(4)  A  road  crosses  contour  lines;  how  can  you  tell  whether 
it  is  up  hill  or  down? 

(5)  Find  an   up-hill  road  on  the   east  side   of   the 

River.     Locate  it. 

(6)  How  many  miles  is  it  from  the  center  of to  the 


30     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

center  of  -     — ?     (Use  a  measure  and  compute  from  the 
scale  on  the  map.) 

(7)  Does    the  River    cross     any    contour    lines 
between  -     -  and  -    — ? 

(8)  Does  the  highway?    The  railroad? 

(9)  What  do  your  answers  show  in  regard  to  the  elevation 
of  these  two  places? 

(10)  Why  are  roads  more  likely  to  follow  than  to  cross 
contour  lines? 

(11)  What  is  the  significance  of  the  straight  lines  crossing 
the  map  from  north  to  south? 

(12)  How  much  of  the  surface  of  the  earth  is  included  in 
this  map?     (Answer  in  degrees  or  parts  of  a  degree.) 

EXERCISE    XXII    (Textbook  §  259) 
STUDY  OF  A  STREAM  AND  ITS  VALLEY 

PLACE  OF  WORK:  Any  locality  where  a  stream,  prefer- 
ably a  brook,  can  be  studied  for  a  length  of  half  a  mile  or  so. 
(A  teacher  can  usually  indicate  an  accessible  stream  and 
perhaps  accompany  the  class  to  visit  it.) 

DIRECTIONS  FOR  WORK:  Begin  at  the  lower  end  of  the 
portion  of  the  stream  selected  (at  the  mouth,  if  possible), 
and  make  notes  on  the  following  points: 

(1)  The  direction  and  velocity  of  the  current. 

(2)  The  character  of  the  banks,  whether  alike  in  material 
and  form  on  both  sides. 

(3)  Evidences  of  erosion  or  deposit. 

(4)  Signs  which  tell  of  higher  water  earlier  in  the  season. 
Follow    the    stream    toward    its    source,    observing    any 

changes  in  any  of  the  respects  observed.. 

(5)  Is  the  course  of  the  stream  straight  or  wandering? 

(6)  Is  its  valley  broad  or  narrow? 

(7)  Has  it  any  tributaries? 

(8)  Are  there  rapids  or  falls  at  any  place? 


LABORATORY  MANUAL  31 

(9)  Are  there  islands?     If  so,  were  they  formed  by  deposit 
by  the  stream? 

(10)  Has  the  stream  or  its  valley  been  altered  in  any  way 
by  man? 

RESULTS 

Write,  in  descriptive  form,  an  account  of  this  stream  so 
far  as  your  notes  give  you  information.  Do  not  try  to 
follow  the  exact  order  of  the  points  called  for  in  your  notes. 

EXERCISE    XXIII    (Textbook  §  272) 

THE   WATER   SUPPLY   OF   A   CITY  OR  TOWN 

MATERIALS:  The  annual  report  of  a  city  or  town  from 
the  Board  of  Water  Commissioners  or  the  Water  Depart- 
ment, annual  report  of  the  Board  of  Health,  daily  news- 
papers. 

(1)  Where  does  the  water  supply  of  your  city  or  town 
come  from? 

(2)  How  is  the  business  of  supplying  the  water  attended 
to? 

(3)  How  is  the  expense  paid? 

(4)  How  is  the  amount  of  water  used  in  each  building 
ascertained? 

(5)  What  is  the  price  of  water  to  the  consumer? 

(6)  What  are  the  uses  of  water  besides  those  of  the  house- 
hold? 

(7)  The  average  amount  of  water  used  per  person  is  greater 
than  it  was  ten  years  ago.     Give  some  reasons. 

(8)  (a)  What   is  a   distributing  reservoir?     (6)  A  water 
main?     (c)  A  gate  in  a  water  main? 

(9)  If  a  distributing  reservoir  is  250  ft.  above  sea  level, 
how  much  fall  is  there  from  it  to  a  part  of  the  town  whose 
level  is  60  ft.? 

(10)  What  advantage  would  there  be  in  a  greater  fall? 


32     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

(11)  What  is  meant  by  "the  catchment  basin"  of  a  reser- 
voir? 

(12)  What  precautions  are  needed  to  keep  the  reservoir 
water  clean  and  harmless? 

(13)  A  community  now  uses  about  8  million  gallons  a  day, 
which  is  more  than  its  present  system  can  supply  in  a  dry 
season.     What  must  be  the  situation  of  a  basin  that  would 
furnish  more  water  to  be  turned  into  the  present  distributing 
reservoir? 

(14)  How  can  water  be  safely  transferred  from  one  reser- 
voir to  the  other? 

(15)  Supposing  a  river  or  a  mountain  lay  between  the  two 
reservoirs,  how  could  those  obstacles  be  overcome? 


EXERCISE    XXIV    (Textbook  §  279) 
THE  WHEAT  SEEDLING 

APPARATUS:  A  piece  of  clean  blotting  paper,  colored 
preferred;  a  plate  or  saucer;  a  tumbler;  some  wheat  seeds, 
morning  glory  seeds,  or  any  other  garden  seeds  of  moderate 
size. 

DIRECTIONS  FOR  WORK:    Soak  20  seeds  for  24  hours. 

(1)  Make  a  drawing  of  a  dry  seed. 

(2)  Make  a  drawing  of  the  seed  which  changed  the  most 
while  soaking. 

(3)  Select  twelve  of  the  most  perfect  seeds  and  place  them 
on  damp  blotting  paper  on  a  plate  under  an  inverted  tumbler. 
If  after  a  day  or  two  the  paper  begins  to  look  dry,  put  a 
few  drops  of  water  on  the  corners  and  the  moisture  will 
spread.     The  paper  should  be  kept  moist,  not  wet.     Examine 
and  record  observations  from  time  to  time.     Do  not  remove 
the  tumbler. 

(4)  Bring  the  paper  with  the  seeds  to  school  after  five 
days. 


LABORATORY  MANUAL  33 

RESULTS 

Answer  the  following  questions  from  your,  own  observa- 
tions : 

1.  What  was  the  first  sign  of  life  which  the  seeds  showed? 

2.  How  many  days  after  the  seeds  were  soaked  did  this 
change  occur? 

3.  How  many  roots  sprang  from  a  single  seed  at  first? 

4.  How  many,  by  the  end  of  the  time  given  for  the  experi- 
ment? 

5.  Did  the  roots  start  from  about  the  same  place  or  from 
very  different  places? 

6.  Describe  the  surface  of  a  single  root. 

7.  What  is  the  color  of  young  roots? 

8.  What  else  seemed  to  come  from  the  seed  besides  the 
roots? 

9.  What  color  was  that  body? 

EXERCISE    XXV    (Textbook  §  298) 
!•  TUDY  OF  THE  ROOTS  OF  A  PLANT 

MATERIALS:  A  seedling  plant  grown  from  a  bean  or  pea; 
a  low  wide-mouthed  bottle  containing  water;  a  slender 
stick  a  few  inches  long. 

DIRECTIONS  FOR  WORK:  Do  not  remove  any  part  of  the 
plant.  In  pulling  it  from  the  ground,  loosen  the  soil  around 
the  roots  with  a  slender  stick.  Leave  the  plant  in  a  bottle 
of  water  at  the  close  of  the  exercise. 

(1)  Name  the  organs  of  the  plant  which  you  see  above 
ground. 

(2)  What  plant  organ  is  below  the  ground? 

(3)  Try  to  pull  up  a  plant  without  breaking  it.     Why  is 
this  a  difficult  task? 

(4)  Where  does  the  plant  sometimes  break  in  your  attempt 
to  pull  it  up? 


34     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

(5)  Can  you  pull  up  the  entire  plant  without  breaking  any 
part  of  it,  if  you  are  careful? 

(6)  From  this  observation  (No.  5),  what  do  you  conclude 
to  be  one  of  the  uses  of  roots  to  the  plant? 

(7)  Are  the  pulled  roots  clean? 

(8)  What  is  their  color  before  washing? 

(9)  How  do  the  roots  look  after  they  have  been  washed 
in  the  bottle? 

(10)  Can  you  account  for  this  by  recalling  the  description 
of  root  hairs,  or  those  on  the  young  plant  which  you  studied 
at  home? 

(11)  Is  one  root  larger  and  thicker  than  the  others? 

(12)  If  so,  how  does  it  seem  to  be  related  to  the  stem? 

(13)  What  position  do  the  small  roots  have  in  relation  to 
the  large  root? 

(14)  What  would  the  roots  of  your  plant  measure  if  cut 
off  and  placed  end  to  end?     (Measure  two  or  three  roots 
and  then  estimate  the  total  root  length.) 


EXERCISE    XXVI    (Textbook  §  300) 
STUDY  OF  THE  STEM  AND  LEAVES  OF  A  PLANT 

MATERIALS:  The  same  plant  used  in  the  previous  exer- 
cise; it  should  be  kept  in  a  bottle 'with  enough  water  to 
cover  the  roots. 

(1)  Make  a  drawing  of  the  plant,  on  the  first  page  of  your 
notebook  sheet. 

(2)  What  organs  are  borne  on  the  stem? 

(3)  What  organ  serves  as  a  connection  between  root  and 
leaves? 

(4)  What,  then,  do  you  conclude  to  be  two  uses  for  stems? 

(5)  How  would  a  plant  change  in  appearance  if  the  soil 
should  remain  dry  for  a  short  time? 

(6)  Then  if  the  soil  is  watered,  what  is  the  result? 


J 


LABORATORY  MANUAL  35 

(7)  What,  then,  is  the  chief  agent  in  keeping  young  stems 
rigid? 

(8)  Each  group  constitutes  a  leaf.     How  many  leaves  are 
there  on  your  plant? 

(9)  Do  the  leaves  shade  each  other  much  or  little? 

(10)  How  does  the  arrangement  of  leaves  on  the  stem 
affect  the  shading? 

(11)  Hold  the  leaf  up  to  the  light  and  describe  the  distribu- 
tion of  veins. 

(12)  Describe  a  cell  from  the  interior  of  a  leaf  -as  seen 
under  the  compound  microscope.     (This  should  be  arranged 
by  the  teacher.) 

(13)  Examine  with  the  microscope  a  portion  of  the  exterior 
of  the  leaf,  showing  the  leaf  pores.     Describe  what  you  see. 


EXERCISE    XXVII   (Textbook  §  301) 
ONE  FUNCTION  OF  LEAVES 

MATERIALS:  A  plate  or  saucer;  leaves  from  a  growing 
plant;  balances;  a  thin  sheet  of  rubber;  a  potted  plant; 
a  glass  jar  or  a  box  with  one  glass  side,  large  enough  to 
cover  the  plant. 

DIRECTIONS  FOR  WORK: 

(1)  Weigh  the  dish.     Place  several  leaves  from  a  growing 
plant  in  the  dish  and  weigh  them  together,  to  .1  g.     Leave 
the  dish  uncovered  in  a  moderate  temperature  for  24  hours 
and  weigh  again.     Continue  this  for  several  days,  recording 
each  weight  taken. 

(2)  Cover  the  pot  and  the  earth  around  the  stem  of  a 
growing  plant  closely  with  a  sheet  of  rubber.     Place  the 
plant  thus  prepared  under  a  dry  glass  cover  and  leave  it 
standing.     From  time  to  time,  observe  any  change  occurring 
under  the  glass. 

If  the  plant  is  in  a  warm  room,  cool  the  glass  after  24 


36     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

hours,  by  opening  a  window  near  it  or  laying  upon  it  for  a 
few  minutes  a  cloth  wrung  out  in  cold  water. 

1.  Weight  of  the  dish g. 

(a)  "      "    "      "  and  leaves  g. 

(6)  "      "     "       "  "          "  g. 

(c)  "      "    "      "  "         "  g. 

(d)  "      "    "      "  "         "  g. 

RESULTS 

1.  What  change  in  the  weight  of  the  leaves  occurred? 
What  do  you  think  was  the  cause  of  the  change? 

2.  Would  there  be  as  great  a  change  in  the  weight  of 
leaves  left  on  a  plant?     Why? 

3.  What  per  cent  of  the  original  weight  was  lost  the 
first  day?     Was  it  the  same  per  cent  every  day? 

4.  Supposing  no  further  change  to  occur  after  you  finished 
weighing,  from  your  figures  calculate  the  per  cent  of  weight 
of  water  in  green  leaves. 

5.  In  Case  2,  why  should  the  pot  be  enclosed  in  rubber? 

6.  What  was  the  evidence  of  escape  of  water  from  the 
plant  leaves? 

7.  In  what  form  did  the  water  escape?    Tell  how  you 
know. 

8.  Where  does  the  water  enter  the  plant? 

9.  What   becomes   of   the   mineral   matter   dissolved   in 
water  which  plants  take  up? 

10..  What  function  of  leaves  has  this  experiment  illustrated? 

EXERCISE    XXVIII    (Textbook  §  307) 
TEST  FOR  FOOD  MATERIAL  IN  SEEDS 

MATERIALS:  Concentrated  nitric  acid;  ammonia  solu- 
tion; solution  of  iodine;  some  means  of  warming  and  press- 
ing (flatiron) ;  various  seed  foods  such  as  oatmeal,  peanuts, 
beans,  nuts. 


LABORATORY  MANUAL  37 

DIRECTIONS  FOR  WORK  : 

(1)  To  test  for  proteids:  Add  a  little  nitric  acid  to  crushed 
seeds;   after  a  minute  rinse  with  water  and  add  a  few  drops 
of  ammonia  solution.     A  yellow  color  where  the  acid  acted 
shows  that  a  proteid  is  present.     The  deeper  the  color,  the 
greater  the  quantity  of  proteid. 

(2)  To  test  for  starch.     Break  open  the  seeds  (if  whole) 
and  boil  them.     Then  add  a  drop  of  iodine  to  the  seed  or 
even  to  the  water  in  which  it  was  boiled.     A  dark  blue 
color  shows  the  presence  of  starch. 

(3)  To  test  for  oil.     Place  the  seeds  between  two  pieces  of 
soft  paper  and  press  them  with  a  warm  iron.     After  a  little 
while,  remove  the  iron,  shake  off  the  seed,  and  hold  the 
paper  toward  the  light.     A  translucent  spot  (in  this  case,  a 
grease  spot)  shows  oil  to  be  present. 

Effect  of  Application  of 
Seeds  ( Nitric  Acid  Iodine  Warmth  and  Pressure 

\  Ammonia 
Oatmeal 
Wheat  Cereal 
Peanuts 
Beans 
Peas 

Corn  (popped) 
Any  nut 


EXERCISE    XXIX    (Textbook  §  312) 
STUDY  OF  A  FLOWER 

MATERIALS:  Flowers,  like  the  tulip  or  Easter  lily,  for  a 
first  exercise;  needles  in  wooden  handles  or  long  slender 
pins;  a  sharp  knife.  (Sweet  peas,  primroses,  or  geraniums 
[single]  are  a  little  less  simple  and  might  be  substituted 
or  taken  later.) 


38     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

DIRECTIONS  FOR  WORK:     Examine  the  whole  flower  and 
write  fully  the  answers  to  the  following  questions: 

(1)  What  is  the  color  of  the  outermost  part  of  the  flower? 

(2)  (a)  Of  how  many  parts  or  -sepals  is  it   composed? 
(b)  Are  they  joined  together? 

(3)  In  what  respects  are  the  sepals  similar? 

(4)  What  is  the  color  of  the  next  circle  of  parts  of  the 
flower? 

(5)  (a)  Of  how  many  parts  or   petals  is    it  composed? 
(b)  Are  they  entirely  separate? 

(6)  In  what  respects  are  the  petals  alike? 

(7)  Are  any  parts  of  the  flower,  besides  the  sepals  and 
petals,  visible?     If  so,  where  are  they? 

(8)  Carefully  pull  off  the  sepals  and  the  petals,  one  at  a 
time;    examine  them  and  lay  them  down  on  your  paper. 
Make  a  drawing  of  one  of  each. 

(9)  How  many  yellow  or  brown  bodies,  anthers,  do  you 
find  attached  to  delicate  stems,  stamens,  near  the  middle  of 
the  flower? 

(10)  Pull  off  these  stamens.    Prick  open  one  of  the  anthers. 
What  do  you  find  in  it? 

(11)  How  many  organs  now  remain?     Describe  the  pistil, 
which  is  left  in  the  center  of  the  flower. 

(12)  Cut  across  this  last  organ  at  its  largest  place.    De- 
scribe what  you  find  inside. 


EXERCISE    XXX    (Textbook  §  316) 
STUDY  OF  A  SEED 

MATERIALS:  A  dry  bean;  one  that  has  been  soaked  in 
water  24  hours;  one  that  has  been  on  moist  paper  or  moss 
for  a  few  days;  a  bean  plant  having  several  leaves;  a  dried 
or  fresh  pod  containing  beans. 


LABORATORY  MANUAL  39 

DIRECTIONS  FOR  WORK:  Number  all  drawings  and  the 
description  or  answer  called  for,  to  correspond  with  direc- 
tions. 

(1)  Lay  a  dry  bean  on  your  paper  and  draw  its  outline  as 
seen  from  the  broad  side.     Compare  length  and  width. 

(2)  Compare  the  thickness  of  the  bean  with  the  width. 

(3)  Describe  the  color.     Is  it  uniform? 

(4)  Find  a  rough,  light  spot  on  the  bean  and  describe  its 
location. 

(5)  What  does  this  tell  of  the  previous  history  of  the  seed? 
(Look  at  the  beans  in  the  pod,  if  necessary.) 

(6)  Examine  a  soaked  bean  and  compare  it  with  a  dry 
bean  as  to  size  and  color.     Can  you  find  the  light  spot? 

(7)  Make  a  lengthwise  scratch  with  a  pin  in  the  coat  of 
the  soaked  bean  on  the  side  farthest  removed  from  the  light 
spot.     Deepen  the  scratch  until  the  coat  is  cut  through  and 
then  remove  the  coat.     The  contents  of  the  coat  is  termed 
the  embryo.     How  many  large  parts  or  organs  are  readily 
distinguishable? 

(8)  How  are  these  large  organs  or  seed  leaves  held  to- 
gether? 

(9)  Carefully  break  off  one  of  the  seed  leaves.     Do  you 
find  something  between  them?   This  is  a  leaf  bud;  describe 
the  number  of  parts,  their  shape,  and  their  attachment  to 
another  organ  of  the  embryo. 

(10)  Draw  separately  each  of  the  'organs  of  the  embryo. 
Number  the  pointed  body  (the  root)   1;    the  seed  leaves 
2   and   3;  their    connection  with    the    stem  4;     the    leaf 
bud  5. 

(11)  Using  a  pin,  try  to  spread  out  the  tiny  organs  which 
you  found  in  Case  9.     What  is  their  shape? 

(12)  Examine  and  make  a  drawing  of  a  soaked  bean  seed 
which  has  been  lying  on  moist  blotting  paper  or  in  damp 
moss  for  a  few  days.     Number  the  parts  shown  in  the  draw- 
ing to  correspond  with  the  parts  of  the  embryo. 


40     FIRST  YEAR  COURSE  IN  GENERAL  SCIENCE 

(13)  Examine  a  bean  plant  growing  in  a  pot  in  the  school- 
room. What  visible  organs  of  this  plant  correspond  to 
organs  of  the  embryo  in  the  seed? 


EXERCISE    XXXI    (Textbook  §  339) 
STUDY  OF  A  FISH 

MATERIALS:  A  live  fish  in  a  jar  of  water.  Goldfish  can 
be  purchased  for  a  small  sum,  if  minnows  or  other  common 
fish  cannot  be  obtained  alive.  If  none  of  these  is  obtainable, 
a  fish  market  might  furnish  smelt,  perch,  or  butterfish  which 
have  not  been  "  dressed." 

DIRECTIONS  FOR  WORK: 

(1)  Compare  the  length,  width,  and  thickness  of  the  fish. 

(2)  Describe  its  shape  as  a  whole.     In  what  respects  is  it 
adapted  to  movement  through  the  water? 

(3)  Compare  its  two  sides. 

(4)  Compare  its  two  ends.     What  advantage  is  there  in 
their  being  different? 

(5)  Compare  the  upper  and  lower  sides  of  the  fish.     Is  the 
same  side  always  uppermost? 

(6)  The  head  extends  from  the  tip  of  the  snout  to  the 
hinder  part  of  the  flap  on  the  sides,     (a)  How  many  times 
the  length  of  the  head  is  the  length  of  the  body?     (6)  Is 
there  a  neck? 

(7)  Describe  the  shape  of  a  fin,  stating  the  position  of  the 
fin  selected. 

(8)  (a)  Locate  all  the  fins,     (b)  How  are  the  fins  stiffened? 

(9)  (a)  Where  must  be  placed  the  muscle  that  moves  the 
tail  to  the  right?     (6)  Where  the  muscle  that  moves  it  to 
the  left?     (c)  What  name  is  given  to  a  pair  of  muscles  so 
related? 

(10)  The  flaps  on  the  side  of  the  head  are  the  gill  covers. 
Describe  their  movements  and  tell  why  they  move. 


LABORATORY  MANUAL  41 

(11)  Describe  the  appearance  of  the  eyes. 

(12)  What  advantages  result  from  the  position  of  the  eyes? 

(13)  (a)  Does  the  fish  have  eyelids?     (6)  How  are  the  eyes 
protected? 

(14)  Where  are  the  nostril  openings? 

(15)  Where  is  the  anus  or  vent  for  indigestible  residue? 


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